Article with gradient property and processes for selective etching

ABSTRACT

An article includes a substrate; and a coating disposed on the substrate that includes a microporous layer; a gradient in a density of a volume of the microporous layer, and a plurality of dendritic veins that are anisotropically disposed in the coating. A process for forming a coating includes disposing an activating catalyst on a substrate; introducing an activatable etchant; introducing an etchant oxidizer, performing an oxidation-reduction reaction between the substrate, the activatable etchant, and the etchant oxidizer in a presence of the activating catalyst, the oxidation-reduction reaction occurring in a liquid medium including the activatable etchant; and the etchant oxidizer, forming an etchant product comprising atoms from the substrate; removing a portion of the etchant product from the substrate; and forming a dendritic vein in the substrate to form the coating, the dendritic vein being anisotropically disposed in the coating.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/928,090 filed Jan. 16, 2014, the disclosure ofwhich is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with United States government support from theNational Institute of Standards and Technology. The government hascertain rights in the invention.

BACKGROUND

A density gradient in silicon can be made by deep reactive ion etchingor dicing a silicon wafer with a dicing saw. These methods may provide arelatively course gradient and may not be suited for creating a densitygradient in a curved surface.

The art is receptive to articles and processes that provide densitygradients in a material.

BRIEF DESCRIPTION

The above and other deficiencies are overcome by, in an embodiment, anarticle comprising: a substrate; and a coating disposed on the substratethat comprises: a microporous layer; a gradient in a density of a volumeof the microporous layer, and a plurality of dendritic veins that areanisotropically disposed in the coating.

Further disclosed is a process for forming a coating, the processcomprising: disposing an activating catalyst on a substrate; introducingan activatable etchant; introducing an etchant oxidizer; performing anoxidation-reduction reaction between the substrate, the activatableetchant, and the etchant oxidizer in a presence of the activatingcatalyst, the oxidation-reduction reaction occurring in a liquid mediumcomprising: the activatable etchant; and the etchant oxidizer; formingan etchant product comprising atoms from the substrate; removing aportion of the etchant product from the substrate; and forming adendritic vein in the substrate to form the coating, the dendritic veinbeing anisotropically disposed in the coating.

Additionally disclosed is a process for forming a coating, the processcomprising: disposing an activating catalyst on a substrate; introducingan activatable etchant; subjecting the activating catalyst and theactivatable etchant to an electric potential; performing anelectrochemical reaction between the substrate and the activatableetchant in a presence of the catalyst and the electric potential, theelectrochemical reaction occurring in a liquid medium comprising: theactivatable etchant; and the etchant oxidizer, forming an etchantproduct comprising atoms from the substrate; removing a portion of theetchant product from the substrate; and forming a plurality of dendriticveins in the substrate to form the coating, the plurality of dendriticveins being anisotropically disposed in the coating.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 shows a top view of an article;

FIG. 2 shows a cross-section of the article shown in FIG. 1;

FIG. 3 shows a top view of an article;

FIG. 4 shows a cross-section of the article shown in FIG. 3;

FIG. 5 shows a cross-section of an article;

FIG. 6 shows a cross-section of an article;

FIG. 7 shows a micrograph of a cross-section of an article;

FIG. 8 shows an enlarged view of a portion of the article shown in FIG.7;

FIG. 9 shows a top view of an article;

FIG. 10 shows a cross-section of the article shown in FIG. 9;

FIG. 11 shows a cross-section of an article;

FIGS. 12A, 12B, and 12C shows formation of an etch void in a substrate;

FIG. 13 show a plurality of activating catalysts disposed on a substrateand having different etch rates;

FIG. 14 shows a plurality of activating catalysts that have differentsizes;

FIG. 15 shows plurality of etch voids disposed in a substrate and aplurality of different activating catalyst disposed in various etchvoids;

FIGS. 16A, 16B, 16C, and 16D show formation of an etch void in asubstrate;

FIG. 17 shows formation of a deposit disposed on a substrate;

FIGS. 18A, 18 B, 18 C, 18 D, 18E, and 18F show formation of a depositdisposed on a substrate and secondary substrate;

FIGS. 19A, 19B, 19C, and 19D show micrographs of etch voids disposed ina substrate according to Example 1;

FIGS. 20A, 20B, 20C, and 20D show micrographs of etch voids disposed ina substrate according to Example 1;

FIGS. 21A, 21B, 21C, and 21D show micrographs of etch voids disposed ina substrate according to Example 1;

FIG. 22 shows a graph of etch depth versus etch time for data accordingto Example 1, Example 2, and Example 1;

FIGS. 23A, 23B, and 23C show graphs of etch depth versus etch time fordata according to Example 1, Example 2, and Example 1;

FIG. 24 shows a graph of etch depth and etch rate versus etchtemperature according to Example 1;

FIG. 25 shows a micrograph of an etch void in a substrate according toExample 2;

FIGS. 26A and 26B show a micrograph of an etch void in a substrateaccording to Example 3;

FIGS. 27A and 27B show a micrograph of an etch void in a substrateaccording to Example 3;

FIGS. 28A and 28B respectively show a micrograph of an etch void in asubstrate and a deposit on the etch void according to Example 4; and

FIGS. 29A, 29B, 29C, and 29D show a micrograph of formation of a depositaccording to Example 5.

DETAILED DESCRIPTION

A detailed description of one or more embodiments is presented herein byway of exemplification and not limitation.

It has been discovered that a coating includes a gradient in a densityof a volume can be an antireflective coatings over a wide range ofincident wavelengths. Advantageously, the coating is applicable toapplications such as an electromagnetic detector or electromagneticabsorber. The coating minimizes an amount of photons reflecting from thecoating. The gradient can vary uniformly over a thickness of thecoating. Additionally, a one-dimensional, two-dimensional, orthree-dimensional nano-sized or micron sized etch void can be formed ina substrate from an activating catalyst in combination with a liquidmedium or a vapor composition. An etch rate, feature resolution, or etchpath of the activating catalyst is controllable to form theone-dimensional, two-dimensional, or three-dimensional etch void. Suchan etch void can have a selectable aspect ratio or nanometer resolution.Further, the deposit can be formed on a substrate through depositionfrom the activating catalyst and vapor deposition composition.

According to an embodiment, an article includes a substrate and acoating disposed on the substrate. The coating includes a microporouslayer, a gradient in a density of a volume of the microporous layer, anda plurality of dendritic veins that are anisotropically disposed in thecoating. In an embodiment, the coating is an antireflective coating.According to an embodiment, the substrate and coating independentlyinclude a semiconductor material. The semiconductor material includes anelement from group III, group IV, group V of the periodic table, or acombination comprising at least one of the foregoing elements. Thesubstrate and the coating can be an identical semiconductor material.

In an embodiment, a process for forming a coating includes disposing anactivating catalyst on a substrate, introducing an activatable etchant,introducing an etchant oxidizer. The process also includes performing anoxidation-reduction reaction between the substrate, the activatableetchant, and the etchant oxidizer in a presence of the activatingcatalyst. The oxidation-reduction reaction can occur in a liquid medium.The liquid medium includes the activatable etchant and the etchantoxidizer. In an embodiment, the process further includes forming anetchant product that includes atoms from the substrate, removing aportion of the etchant product from the substrate, and forming adendritic vein in the substrate to form the coating. According to anembodiment, the dendritic veins is anisotropically disposed in thecoating. In a particular embodiment, the process further includesforming a gradient in a density of a volume of the coating.

According to an embodiment, a process for forming a coating includesdisposing an activating catalyst on a substrate, introducing anactivatable etchant, subjecting the activating catalyst and theactivatable etchant to an electric potential, and performing anelectrochemical reaction between the substrate and the activatableetchant in a presence of the catalyst and the electric potential. Theelectrochemical reaction occurs in a liquid medium that includes theactivatable etchant and the etchant oxidizer. The process also includesforming an etchant product comprising atoms from the substrate, removinga portion of the etchant product from the substrate, and forming aplurality of dendritic veins in the substrate to form the coating. Theplurality of dendritic veins is anisotropically disposed in the coating.During the process, a temperature of the substrate during theelectrochemical reaction can be less than 150° C.

In an embodiment, a process for etching includes disposing an activatingcatalyst on a substrate, providing a vapor composition comprising anetchant oxidizer, an activatable etchant, or a combination thereof,contacting the activating catalyst with the etchant oxidizer, contactingthe substrate with the activatable etchant, performing anoxidation-reduction reaction between the substrate, the activatableetchant, and the etchant oxidizer in a presence of the activatingcatalyst and the vapor composition, forming an etchant productcomprising atoms from the substrate, and removing the etchant productfrom the substrate to etch the substrate. The process further includesadjusting a position of the activating catalyst in the substrate orforming an etch void in the substrate as a result of removing theetchant product from the substrate. A shape of the etch void correspondsto a cumulative position of the activating catalyst in the substrate orformation of an additional etch void produced proximate to a peripherallocation of the cumulative position of the activating catalyst. Withoutwishing to be bound by theory, it is believed that in this mannersecondary etching occurs when a hole (h⁺) injection rate at anactivating catalyst-substrate interface is larger than an etch rate ofthe substrate beneath the activating catalyst. Such a condition canprovide additional etching in a region surrounding the activatingcatalyst to form a region of microporous silicon proximate to an etchpath. The process further can include controlling a rate of forming theetch product.

According to an embodiment, a process for depositing a metal includesdisposing an activating catalyst on a substrate, contacting the catalystwith a metal cation from a vapor deposition composition, contacting thesubstrate with a reducing anion from the vapor deposition composition,performing an oxidation-reduction reaction between the metal cation andthe reducing anion in a presence of the activating catalyst, and forminga metal from the metal cation to deposit the metal on the substrate. Theprocess further includes forming the vapor deposition composition bycombining the metal cation from a first source and the reducing anionfrom a second source and providing the vapor deposition composition tothe substrate and the activating catalyst for contacting the activatingcatalyst with the metal cation and contacting the substrate with thereducing anion. The process also includes forming the vapor depositioncomposition that includes the metal cation and the reducing anion andproviding the vapor deposition composition to the substrate and theactivating catalyst for contacting the activating catalyst with themetal cation and contacting the substrate with the reducing anion. Theprocess further includes dissociating a primary reagent to form themetal cation and the reducing anion, forming the metal cation and thereducing anion in a liquid state in response to dissociating the primaryreagent, and volatilizing the metal cation, the reducing anion, or acombination comprising at least one of foregoing to form the vapordeposition composition.

In an embodiment, a system for depositing a metal includes an activatingcatalyst to deposit on a substrate and a primary reagent to form a metalcation to deposit on the substrate as a metal and a reducing anion toprovide electrons to the activating catalyst, the metal cation, thesubstrate, or a combination thereof. The primary reagent forms the metalcation and the reducing anion in response to being subjected to adissociating condition.

In an embodiment, as shown in FIG. 1 (top view of article 2), article 2includes etch void 6 disposed in substrate 4. Etch void 6 extends from asurface of article 2 to a depth below the surface of article 2. FIG. 2shows a cross-section along line A-A of article 2. A transverse crosssectional shape of etch void 6 can be circular, ellipsoidal, polygonal,irregular, and the like. A plurality of etch voids 6 can be disposed insubstrate 4 and arranged to have a same spacing between adjacent etchvoids 6. In some embodiments, etch voids 6 are arranged to have adifferent spacing between adjacent etch voids 6 as shown for top view ofarticle 2 in FIG. 3. Here, adjacent etch voids 6 can be separated byfirst spacing S1, second spacing S2, third spacing S3, and the like,wherein the spacings (S1, S2, S3) are different from one another.

Depths of etch voids 6 in article 2 can be the same or different.According to an embodiment, depths of etch voids 6 are the same. In acertain embodiment, the depth of some or all of etch voids 6 isdifferent from one another. With reference to FIG. 4, which is across-sectional view along line B-B of article 2 shown in FIG. 3, etchvoids 6 can have different depths such as first depth D1, second depthD2, or third depth D3.

Widths of etch voids 6 in article 2 can be the same or different.According to an embodiment, widths of etch voids 6 are the same. In acertain embodiment, the width of some or all of etch voids 6 isdifferent from one another. In an embodiment is shown in FIG. 5, whichis a cross-section of article 2, etch voids 6 can have different widthssuch as first width W1, second width W2, or third width W3.

In addition to a transverse cross-sectional shape, etch void 6 can havea longitudinal cross-sectional shape that is the same or different thanthe transverse cross-sectional shape of etch void 6. With reference toFIG. 6, etch voids 6 are bounded by wall 10 and exposed to an exteriorof article 2. Wall 10 can be curved, straight, or combination thereof.Etch void 6 can have wall 10 that is smooth or angular. An opening ofetch void six can be larger in a particular dimension than any otherportion of etch void 6 or smaller in a particular dimension than theother portion of etch void 6. Exemplary transverse cross-sectionalshapes of etch void 6 include asymmetrical 8, spherical 12, serpentine14, apical 16, frustoconical 18, branching 19, and the like.

In an embodiment, a plurality of etch voids 6 are disposed in article 2to form coating 22 as shown in FIG. 7, which shows a micrograph ofarticle 2. Coating 22 is disposed on substrate 4. Here, etch voids 6 areanisotropically arranged as dendritic veins 24 such that a top surfaceof coating 22 has first interface 23 with an external environment suchas air 26. Additionally, dendritic veins 24 have a greatest numberdensity at first interface 23. Second interface 25 between coating 22and substrate 4 occurs where wall 10 of etch voids 6 and substrate 4meet. As such, second interface 25, as shown in FIG. 7, is irregular,i.e., nonplanar on a selected scale such as a nanometer or micrometerscale. Coating 22 also includes a microporous layer that is a samematerial as substrate 4. In an embodiment, dendritic veins 24 areproduced in substrate 4 by forming the microporous layer, which has aplurality of pores in which some of the pores interconnect to fromdendritic vein 24.

In an embodiment, the number density of dendritic veins 24 decreasesfrom first interface 23 to second interface 25. As a result, coating 22has a gradient in a density of the microporous layer. The density of themicroporous layer and coating 22 is greatest at second interface 25, andthe density of microporous layer and coating 22 is released at firstinterface 23. The gradient in the density of the volume of themicroporous layer varies uniformly from first interface 23 to secondinterface 25. Accordingly, a refractive index of coating 22 varies withthe gradient in the density of the volume of the microporous layer suchthat coating 22 also has a gradient in its refractive index from firstinterface 23 two second interface 25. Moreover, a refractive index ofcoating 22 at first interface 23 can be selected to match a refractiveindex of the external environment such as air 26. Further, a refractiveindex of coating 22 at second interface 25 can be selected to match arefractive index of substrate 4. As a result, article 2 includes coating22 that has a refractive index that uniformly changes from a firstrefractive index at first interface 23 to a second refractive index atsecond interface 25. The first refractive index or the second refractiveindex can be tuned respectively to match the refractive index of theexternal environment (e.g., air 26) and substrate 4 by tailoring theformation of dendritic veins 24. According to an embodiment, thegradient in the refractive index and the density of the volume of themicroporous layer is selectively tunable by virtue of formation ofdendritic veins 24.

FIG. 8 shows an enlarged view of portion E of article 2 shown in FIG. 7.Here, activating catalyst 28 is shown as a white feature of terminals ofdendritic vein 24. Activating catalyst 28 provides selective control forproduction of dendritic veins 24 and to select the gradient in thedensity of the volume of the microporous layer of coating 22. As will beexplained, activating catalyst 28 is involved in etching substrate fourto form dendritic veins 24 and may be left disposed in dendritic veins24 or can be removed from dendritic veins 24 in article 2.

Besides forming etch void 6 and dendritic veins 24, activating catalyst28 can be used to form deposit 20 on substrate 4 as shown in a top viewof article 2 in FIG. 9. That is, deposit 20 is a structure disposed onsubstrate 4 and is a product of growth on substrate 4 from activatingcatalyst 28 that serves as a seed site for such growth. A cross-sectionalong line C-C of article 2 is shown in FIG. 10. Here, deposit 20 has anasymmetrical shape although deposit 20 is not limited thereto. In anembodiment, deposit 20 can have a selected shape based on growth ofdeposit 20 on activating catalyst 28.

In some embodiments, deposit 20 is disposed in etch void 6 withinsubstrate 4 at shown in FIG. 11, which is a cross-section of article 2.It is contemplated that deposit 20, etch void 6, substrate 4, or article2 can have an arbitrary shape that can be selected based on controlledprocess conditions.

In an embodiment, substrate 4 includes a semiconductor. An exemplarysemiconductor is an element from group 11, 12, 13, 14, 15, or 16 (IUPACnomenclature, which respectively is identical to group I, II, III, IV,V, or VI) of the periodic table such as a Si, Ga, Ge, As, In, Sn, Sb,Te, At, Hf, Zn, and the like, or a combination thereof. According to anembodiment, substrate 4 is a compound semiconductor such as SiC, SiGe,GaN; a group 13-15 (also referred to as a group III-V) semiconductorsuch as AlSb, AlAs, Aln, AlP, BN, GaSb, GaAs, GaN, GaP, InSb, InAs, InN,InP, and the like; a group 12-16 (group II-VI) semiconductor such asCdSe, CdS, CdTe, ZnO, ZnSe, ZnS, ZnTe, and the like; a group 11-17(group I-VII) semiconductor such as CuCl and the like; a group 14-16(group IV-VI) semiconductor such as PbS, PbTe SnS, and the like; a layersemiconductor such as PbI₂, MoS₂, GaSe, and the like; an oxidesemiconductor such as CuO, Cu₂O, and the like; (Al,Ga)N, (Al,Ga)As,(In,Ga)As, (Al,Ga)Sb, (In,Ga)Sb, as well as nitride, arsenide,antimonide quaternary III-V alloys, or a combination comprising at leastone of the foregoing. Examples of II-VI alloys include, but are notlimited to CdSe, CdTe, CdS, ZnSe, and combinations thereof. Examples ofGroup III-V ternary alloys include, but are not limited to, (Ga,Al)As,(In,Ga)As, and combinations thereof. Exemplary Group III-V quaternaryalloys include (Ga,In)(As,P), (In,Al,Ga)Sb, and the like. ExemplaryGroup III-nitride alloys include (Ga,Al)N, (Ga,In)N, (Al,In)N,(Ga,Al,In)N, and combinations thereof. Quaternary alloys of the abovemay also be employed.

Substrate 4 also can include a supplemental element such as C, H, N, Li,Na, K, Mg, Ca, Sr, Ba, Bi, B, Al, P, S, O, and the like in an amounttypically less than an amount of the semiconductor. In an embodiment,substrate 4 includes silicon, and the silicon is optionally doped.According to an embodiment, the semiconductor is an intrinsicsemiconductor or an extrinsic semiconductor doped with a selecteddopant, e.g., a p-dopant or an n-dopant. In one embodiment, substrate 4includes a p-dopant. In another embodiment, substrate 4 includes ann-dopant. In a particular embodiment, substrate 4 is p-doped Si. In oneembodiment, substrate 4 is n-doped Si. Substrate 4 can be produced from,e.g., commercially available semiconductor grade p-doped Si having aparticular crystalline orientation, e.g., having Miller indices <111>,<100>, and the like. Substrate 4 can be amorphous, polycrystalline, or asingle crystal. In an embodiment, substrate 4 has a stacked structurethat includes a plurality of semiconductor layers such as by formingfilms as SiGe/Si/SiGe/Si on the Si substrate. In some embodiments,substrate 4 includes crystalline domains among amorphous material. In anembodiment, substrate 4 is selected to provide coating 22 by etching ofsubstrate 4 in a presence of activating catalyst 28. According to anembodiment, coating 22 includes a same material as substrate 4. In anembodiment substrate 4 and coating 22 independently include asemiconductor material. 4. In an embodiment, the semiconductor materialincludes an element from group III, group IV, group V of the periodictable, or a combination thereof. In a certain embodiment, substrate 4and coating 22 are an identical semiconductor material. In someembodiments, coating 22 is a different material than substrate 4 suchthat article 2 is a laminate having coating 22 of a first materialdisposed on substrate 4 of a second material.

In a particular embodiment, substrate 4 is selected to supportactivating catalyst 28 for formation of deposit 20.

According to an embodiment, activating catalyst 28 is a metal. Exemplarymetals include elements from transition metal (e.g., group IB, IIB,IIIB, IVB, V, VIB, VII B, VIII), alkali metal (e.g., Na), alkaline earthmetal (e.g., Mg) of the periodic table, including but not limited to,include Zr, Hf, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Tc, Ru, Rh,Pd, Ag, Cd, Ta, W, Re, Os, Ir, Pt, Au, Li, Na, K, Be, Mg, Ca, Sr, Ba,Gd, a compound thereof, an alloy thereof, or a combination thereof. In aparticular embodiment, the metal is platinum, gold, silver, or acombination thereof. Further, the metal can be in any suitable form suchas powder, dust, particle, and the like. In an embodiment, the metal isa nanoparticle. In a further embodiment, the metal is charge neutral inactivating catalyst 28. As used herein, “activating catalyst” refers toa catalyst that has an activity effective to catalyze etching ofsubstrate 4 in presence of the activatable etchant and etchant oxidizeror effective to catalyze formation of deposit 20 on substrate 4 in apresence of a vapor deposition composition.

According to an embodiment, activating catalyst 28 is a low-temperaturecatalyst, which has an activity effective to catalyze etching or metalformation over a broad temperature range or broad pressure range. In anembodiment, activating catalyst 28 is a low-temperature catalyst havingcatalytic activity at a temperature, e.g., from 0° C. to 500° C.,specifically 20° C. to 300° C., and more specifically 20° C. to 150° C.Moreover, activating catalyst 28 effectively catalyzes etching ofsubstrate 4 or deposition of deposit 20 at a low pressure, low numberdensity, or low concentration of etchant oxidizer, activatable etchant,or vapor deposition composition.

Etch void 6 (e.g., dendritic vein 24) is formed from activating catalyst28 and substrate 4 in presence of an activatable etchant an etchantoxidizer. In an embodiment, the activatable etchant is a fluorideetchant. Exemplary fluoride etchants include hydrofluoric acid (HF),buffered oxide etch (BOE), boron hydrogen fluoride (BHF), or otherfluoride complex (e.g., BF₄—*, PF₆—*, CF₃SO₃—*, AsF₆—*, and SbF₆—*,where * represents a chemical compound, species, or support), and thelike.

In a certain embodiment, activating catalyst 28 is a halide source,reactive halide species, β-diketone activatable etchant, and the like.

The halide source is a material that provides a halide atom to interactwith substrate 4 to form etchant product 32 (see FIGS. 12A, 12B, and12C) under reaction conditions in presence of activating catalyst 28.Exemplary halide sources include a metal halide, e.g., TiCl₄, NbCl₅,NbBr₅, TaCl₅, TaBr₅, MoF₆, WF₆, BCl₃, SnCl₄, SnBr₄; organic halogencompound, e.g., CF₂Cl₂, CBr₄, CFCF, and the like; elemental halogen,e.g., F₂, Cl₂, Br₂, or I₂; interhalogens, e.g., FCl, CBr, Cl; hydrogenhalide, e.g., HF, HCl, HBr, or HI; cyanogen halide, or other suitablehalide source including a non-metal halide, e.g., XeF₂PCl₅, and thelike. In some embodiments, the halide source includes a plurality oftypes of halide atoms, e.g., chlorine and fluorine. In some embodiments,the halide source is BCl₃, CF₂Cl₂, NbCl₅, TaCl₅, or WCl₆. An analog orcombination of any of the foregoing can be used as the halide source.

Reactive halide species etch substrate 4 to produce to form etchantproduct 32. Exemplary reactive halide species include a metal halide,metal oxyhalide, metal hydroxyhalide, and the like.

Exemplary β-diketone activatable etchants include β-diketones such asacetylacetone (2,4-pentanedione,), hexafluoroacetylacetone(1,1,1,5,5,5-hexafluoro-2,4-pentanedione), tetramethylheptanedione(2,2,6,6-tetramethyl-3,5-heptanedione),1,1,1,2,2-pentafluoro-6,6-dimethyl-3,5-heptanedione,trifluoroacetylacetone (1,1,1-trifluoro-2,4-pentanedione), combinations,analogs, and the like.

Exemplary etchant oxidizers include hydrogen peroxide (H₂O₂),K₂MnO₄FeNO₃, O₃, CO₂, K₂Cr₂O₇, CrO₃, KIO₃, KBrO₃, NaNO₃, HNO₃, KMnO₄,ethyl ketone peroxide, benzoyl peroxide, acetone peroxide, t-amylperoxybenzoate, t-hexyl peroxybenzoate, 1,3,3,3-tetramethylbutylperoxybenzoate, t-amyl peroxy-m-methylbenzoate, t-hexylperoxy-m-methylbenzoate, 1,1,3,3-tetramethylbutylperoxy-m-methylbenzoate, t-hexyl peroxy-p-methylbenzoate, t-hexylperoxy-o-methylbenzoate, t-hexyl peroxy-p-chlorobenzoate, bis(t-hexylperoxy)phthalate, bis(t-amyl peroxy)isophthalate, bis(t-hexylperoxy)isophthalate, bis(t-hexyl peroxy)terephthalate, tris(t-hexylperoxy)trimellitate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(t-hexylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)cyclododecane,1,1-bis(t-butylperoxy)cyclohexane, 2,2-bis(t-butylperoxy)octane,n-butyl-4,4-bis(t-butylperoxy)butane,n-butyl-4,4-bis(t-butylperoxy)valerate, di-t-butyl peroxide, dicumylperoxide, t-butyl cumyl peroxide,α,α′-bis(t-butylperoxy-m-isopropyl)benzene,α,α′-bis(t-butylperoxy)diisopropylbenzene,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, acetyl peroxide; isobutyrylperoxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide,3,5,5-trimethyl hexanoyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoylperoxide, m-toluoyl peroxide, t-butyl peroxyacetate, t-butylperoxyisophtalate, t-butyl peroxy-2-ethylhexanoate, t-butylperoxylaurate, t-butyl peroxybenzoate, di-t-butyl peroxyisophthalate,2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butyl peroxymaleic acid,t-butyl peroxyisopropylcarbonate, cumyl peroxyoctate, t-butylhydroperoxides, cumene hydroperoxides, diisopropylbenzenehydroperoxides, 2,5-dimethylhexane-2,5-dihydroperoxide, and1,1,3,3-tetramethylbutyl hydroperoxide, and the like.

The liquid composition can include a solvent such as water, an ionicliquid, organic solvent, aqueous solvent, acidic solvent, basic solvent,and the like. The solvent can be selected to effectively solvate ordisperse the activating catalyst, etchant oxidizer, activatable etchant,and the like.

According to an embodiment, deposit 20 (e.g., a metal) is formed onsubstrate 4 in an electroless deposition manner in presence ofactivating catalyst 28 and a vapor deposition composition, whichincludes, e.g., a metal cation. Here, the metal cation can be providedfrom a primary reagent that includes a metal, corresponding to the metalcation. Exemplary primary reagents include a metal alkyl, metal alkylamide, metal alkoxide, metal beta-diketonate, organometallic, metalcarbonyl, metal salt, and the like.

Exemplary metal alkyls include diethyldiselenide, diethylzinc,dimethylaluminum i-propoxide, dimethylcadmium, dimethylmercury,dimethylselenide, dimethylzinc, tetraethylgermane, tetramethylgermane,tetramethyltin, tetra-n-butylgermane,triethyl(tri-sec-butoxy)dialuminum, triethylaluminum, triethylarsine,triethylboron, triethylgallium, tri-i-butylaluminum, trimethylaluminum,trimethylantimony, trimethylarsine, trimethylboron, trimethylgallium,trimethylindium, and the like.

Exemplary metal alkyl amides includebis(p-dimethylamino)tetrakis(dimethylamino)digallium,pentakis(dimethylamino)tantalum(V), tetrakis(diethylamino)titanium,tetrakis(diethylamino)zirconium, tetrakis(dimethylamino)titanium,tetrakis(dimethylamino)zirconium,tris[n,n-bis(trimethylsilyl)amide]yttrium(III),tris(dimethylamino)antimony, tris(dimethylamino)arsine,tris(dimethylamino)phosphine, tris(dimethylamino)silane, and the like.

Exemplary metal alkoxides include aluminum s-butoxide, aluminumethoxide, aluminum i-propoxide, dimethylaluminum i-propoxide,antimony(III) n-butoxide, antimony (III) ethoxide, germanium (IV)ethoxide, hafnium (IV) t-butoxide, hafnium (IV) ethoxide, niobium (V)ethoxide, tantalum(V) ethoxide, tantalum(V) methoxide,tetrabutoxysilane, tetraethoxysilane, tetramethoxysilane, thallium(I)ethoxide, tin(IV) t-butoxide, titanium(IV) n-butoxide, titanium(IV)t-butoxide, titanium(IV) ethoxide, titanium(IV) i-propoxide, vanadium(V)tri-i-propoxy, zirconium(IV) t-butoxide, zirconium(IV)t-butoxide,zirconium(IV) ethoxide, and the like.

Exemplary metal beta-diketonates include aluminum acetylacetonate,aluminum hexafluoroacetylacetonate,bis(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate)barium,bis(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate)calcium,bis(2,2,6,6-tetramethyl-3,5-heptanedionato)barium hydrate

bis(2,2,6,6-tetramethyl-3,5-heptanedionato)barium,bis(2,2,6,6-tetramethyl-3,5-heptanedionato)barium,bis(2,2,6,6-tetramethyl-3,5-heptanedionato)calcium,bis(2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II),bis(2,2,6,6-tetramethyl-3,5-heptanedionato)(1,5-cyclooctadiene)ruthenium(II),bis(2,2,6,6-tetramethyl-3,5-heptanedionato)lead(II),bis(2,2,6,6-tetramethyl-3,5-heptanedionato)magnesium,bis(2,2,6,6-tetramethyl-3,5-heptanedionato)nickel(II),bis(2,2,6,6-tetramethyl-3,5-heptanedionato)strontium,bis(2,2,6,6-tetramethyl-3,5-heptanedionato)strontium,bis(2,2,6,6-tetramethyl-3,5-heptanedionato)zinc, calciumhexafluoroacetylacetonate, cerium(III) trifluoroacetylacetonate,chromium(III) acetylacetonate, chromium(III) hexafluoroacetylacetonate,copper(II) hexafluoroacetylacetonate, copper(II)hexafluoroacetylacetonate, copper(II) trifluoroacetylacetonate,1,5-cyclooctadiene(acetylacetonato)iridium(I),dimethyl(acetylacetonate)gold(III),dimethyl(trifluoroacetylacetonate)gold(III), erbium(III)hexafluoroacetylacetonate, gallium(III) acetylacetonate, indium(III)trifluoroacetylacetonate, iron(III) trifluoroacetylacetonate, lead(II)hexafluoroacetylacetonate, neodymium(III) hexafluoroacetylacetonate,neodymium(III) trifluoroacetylacetonate, platinum(II)hexafluoroacetylacetonate, praseodymium(III) hexafluoroacetylacetonate,praseodymium(III) trifluoroacetylacetonate, rhodium(III)acetylacetonate, samarium(III) trifluoroacetylacetonate, strontiumhexafluoroacetylacetonate, tantalum(V) tetraethoxyacetylacetonate,tantalum(V) (tetraethoxy),tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)niobium(IV),tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)zirconium(IV),2,2,6,6-tetramethyl-3,5-heptanedionato silver(I),2,2,6,6-tetramethyl-3,5-heptanedionato thallium(I), thallium(I)hexafluoroaoetylacetonate, tin (II) acetylaoetonate, tin (II)hexafluoroaoetylacetonate,tris(norbornadiene)(acetylacetonato)iridium(III), tris2,2,6,6)′-tetramethyl-3,5-heptanedionatochromium(III), tris2,2,6,6-tetramethyl-3,5-heptanedionatocobalt(III),tris(2,2,6,6,-tetramethyl-3,5-heptanedionato)erbium(III), tris2,2,6,6§tetramethyl-3,5-heptanedionato indium(III), tris2,2,6,6-tetramethyl-3,5-heptanedionato iron(III), tris2,2,6,6-tetramethyl-3,5-heptanedionato lanthanum(III), and the like.

In certain embodiments, the primary reagent is the organometalliccompound that includes a metallocene, metal carbonyl, or a combinationthereof. According to an embodiment, the organometallic compound candecompose to form numerous reactant products, e.g. a metal cation,reducing anion, or a combination thereof. Such decomposition productscan enter into the gas phase as part of the vapor deposition compositionfor interaction with activating catalyst 28 or substrate 4.

As used herein “organometallic compound” refers to a compound thatcontains a bond between a metal and a carbon atom in a neutral molecule,ion, or radical. In an embodiment, the organometallic compound containsa metal (e.g., a transition metal) with metal-carbon single bonds ormetal-carbon multiple bonds as well as metal complexes with unsaturatedmolecules (metal-xt-complexes). Examples of the organometallic compoundsare sandwich compounds. Such sandwich compounds include full sandwiches,half sandwiches, multidecker sandwiches such as triple deckersandwiches, and inverse sandwiches. The organometallic compound caninclude more than one metal atom, and each metal atom can be a differenta metal element, the same metal element, or a combination thereof. In anembodiment, multiple metal atoms can be bonded to one another inaddition to carbon or bound only to the organic ligand portions of thesandwich compound.

In an embodiment, the ligands of the organometallic compound are thesame or different. Examples of the ligand include alkyl, aryl, hydride,halide, amide, η²-alkene, CO, CS, amine, nitrile, isocyanide, phosphane,alkylidene (CR₂), alkyldiide (CR₂ ²⁻), nitrene (NR), imide (NR²⁻), oxide(O²⁻), alkylidyne (CR), alkyltriide (CR³⁻), η³-allyl, η³-enyl,η³-cyclopropenyl, NO, η⁴-diene, η⁴-cyclobutadiene, η⁵-cyclopentadienyl,η⁶-arene, η⁶-triene, η⁷-tropylium, η⁷-cycloheptatrienyl,η⁸-cyclooctatetraene, or a combination comprising at least one of theforegoing. Here, R represents a functional group selected from hydrogen,alkyl, alkoxy, fluoroalkyl, cycloalkyl, heterocycloalkyl, cycloalkyloxy,aryl, aralkyl, aryloxy, aralkyloxy, heteroaryl, heteroaralkyl, alkenyl,alkynyl, NH₂, amine, alkyleneamine, aryleneamine, alkenyleneamine, andhydroxyl. In addition, the organometallic compound can include variousinorganic ligands, for example, CO₂, and CN, in their neutral or ionicforms.

According to an embodiment, the organometallic compound is a metalcarbonyl. Exemplary metal carbonyls include V(CO)₆, Cr(CO)₆, Mn₂(CO)₁₀,Fe(CO)₅, Fe₂(CO)₉, Fe₃(CO)₁₂, Co₂(CO)₅, Co₄(CO)₁₂, Ni(CO)₄, Mo(CO)₆,Tc₂(CO)₁₀, Ru(CO)₅, Ru₃(CO)₁₂, Rh₄(CO)₁₂, Rh₆(CO)₁₆, W(CO)₆, Re₂(CO)₁₀,Os(CO)₅, Os₃(CO)₁₂, Ir₄(CO)₁₂, and the like. In a non-limitingembodiment, the metal carbonyl is in a liquid state such as Fe(CO)₅.

In an embodiment, the ligand of the organometallic compound is anunsaturated group or molecule, including, for example, η³-allyl,η³-(Z)-butenyl, η³-2-methylpropenyl, η⁴-2-methylidene-propane-1,3-diyl,η⁶-2,3-dimethylidene-butane-1,4-diyl, η⁵-(Z,Z)-pentadienyl,η⁵-cyclopentadienyl (hereinafter “cyclopentadienyl” or “cp”),pentamethyl-η⁵-cyclopentadienyl, η⁵-cyclohexadienyl,η⁷-cycloheptatrienyl, η⁷-cyclooctatrienyl, 1-methyl-η⁵-borole,η⁵-pyrrolyl, η⁵-phospholyl, η⁵-arsolyl, η⁶-boratabenzene, andη⁶-1,4-diboratabenzene.

The ligands of the organometallic compound can be substituted a (e.g.,1, 2, 3, 4, 5, 6 or more) substituents independently selected from ahalide (e.g., F⁻, Cl⁻, Br⁻, I⁻), hydroxyl, alkoxy, nitro, cyano, amino,azido, amidino, hydrazino, hydrazono, carbonyl, carbamyl, thiol, C₁ toC₆ alkoxycarbonyl, ester, carboxyl or a salt thereof, sulfonic acid or asalt thereof, phosphoric acid or a salt thereof, C₁ to C₂₀ alkyl, C₂ toC₁₆ alkynyl, C₆ to C₂₀ aryl, C₇ to C₁₃ arylalkyl, C₁ to C₄ oxyalkyl, C₁to C₂₀ heteroalkyl, C₃ to C₂₀ heteroaryl (i.e., a group that comprisesat least one aromatic ring, wherein at least one ring member is otherthan carbon), C₃ to C₂₀ heteroarylalkyl, C₃ to C₂₀ cycloalkyl, C₃ to C₁₅cycloalkenyl, C₆ to C₁₅ cycloalkynyl, C₅ to C₁₅ heterocycloalkyl, or acombination including at least one of the foregoing, instead ofhydrogen, provided that the substituted atom's normal valence is notexceeded.

The metal of the organometallic compound can be an alkali metal, analkaline earth metal, an inner transition metal (a lanthanide oractinide), a transition metal, or a post-transition metal. In anembodiment, the metal of the organometallic compound is magnesium,aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel,zirconium, ruthenium, hafnium, tantalum, tungsten, rhenium, osmium, or acombination comprising at least one of the foregoing.

In an embodiment, the organometallic compound contains an aromatic ringsuch as an aryl or cyclopentadienyl group. Further, the organometalliccompound can include multiple ring structures that bind to one or moremetal atoms such as fulvalenediyl rings. In a further embodiment, theorganometallic compound is a metallocene, for example, ferrocene,cobaltocene, nickelocene, ruthenocene, vanadocene, chromocene,decamethylmanganocene, decamethylrhenocene, or a combination of at leastone of the foregoing, including dimers and oligomers thereof. As notedabove, the metallocene can be substituted, e.g., as inmethylcyclopentadienyl manganese tricarbonyl. In an alternativeembodiment, the organometallic material can be a compound that containsa four-, five-, six-, seven-, eight-membered ring, or a combinationthereof. Furthermore, the rings in the organometallic compound can betilted so that the metal can accommodate acyclic ligands as well as morethan two rings, for example, W₂(η⁵-C₅C₅)₂(η⁵-C₅H₄)₂H₂.

Metallocene compounds can be obtained commercially or synthesized. Acyclopentadienide or its derivative can be reacted with sodium to formsodium cyclopentadienide. A solution containing the transition metal,for example, a solution of the halide salt of the transition metal, canbe added to the sodium cyclopentadienide to produce the metallocene.Alternatively, substituted metallocenes that are “asymmetrical,” forexample, metallocenes having two different cyclopentadienyl ligands, canbe obtained by reacting equimolar quantities of two differentcyclopentadienides. A further alternative to produce asymmetricalmetallocenes is to react an unsubstituted metallocene with an alkylhalide via Friedel Crafts alkylation to produce mono- and N,N′-dialkylsubstituted metallocenes in the product mixture, the former being theasymmetrical metallocene. Each metallocene can be separated viaseparation technique known in the art such as distillation or flashchromatography. Metallocenes containing two or more substituents in oneor both of the cyclopentadienyl rings may be made as described in U.S.Pat. No. 7,030,257, the disclosure of which is incorporated herein byreference in its entirety.

During the formation of deposit 20 on substrate 4, a metal cation fromthe organometallic material is reduced to a metal with an oxidationstate of zero on substrate 4 by activating catalyst 28. Without wishingto be bound by theory, it is believed that the organometallic materialdissociates whereby a bond between the ligand and the metal is broken inthe organometallic material, and a metal cation is formed from themetal, which becomes part of the vapor deposition composition to beprovided to activating catalyst 28 on substrate 4. The metal cation isreduced to metal with a zero oxidation state at activating catalyst 28.In some embodiments, deposit 20 is an alloy of different metals, wherethe various metals are derived from a plurality of metal cationicspecies from different organometallic compounds. In an embodiment,ferrocene and cobaltocene are used so that a cobalt-iron (alloy) deposit20 is formed. Furthermore, the size and composition of deposit 20 can becontrolled by formation conditions, including temperature, pressure, andchemical concentrations, e.g., metal cation number density in the vapordeposition composition. In an embodiment, the primary reagent is theorganometallic compound, e.g., triethylaluminum, that has a boilingpoint from 100° C. to 150° C. at one atmosphere of pressure.

According to an embodiment, the primary reagent is the metal salt. Here,formation of deposit 20 occurs, in an embodiment, by dissociating theprimary reagent, i.e., the metal salt, into a metal cation and reducinganion from which the vapor deposition composition is composed. The vapordeposition composition then contacts substrate 4 en route to formingdeposit 20 by a reduction-oxidation (redox) reaction involving the metalcation, i.e., reduction of the metal cation to a metallic state asdeposit 20.

The metal salt indirectly provides the metal for producing the deposit20 on substrate 4 by release of a metal cation from the metal salt.According to an embodiment, the metal salt includes a metal and neutralcoordinating organic ligand or coordinating anion. In an embodiment, theligand is an alkyl group, aryl group or other group described above inrelation to the ligand in the organometallic compound. Here, “alkyl”refers to a normal-, secondary-, or tertiary-hydrocarbon having from 1to 12 carbon atoms. Exemplary alkyl groups includes methyl, ethyl,1-propyl, 2-propyl, 1-butyl, 2-methyl-1-propyl(i-Bu), 2-butyl (s-Bu)2-methyl-2-propyl (t-Bu), 1-pentyl (n-pentyl), 2-pentyl, 3-pentyl,2-methyl-2-butyl, 3-methyl-2-butyl, 3-methyl-1-butyl, 2-methyl-1-butyl,1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl,4-methyl-2-pentyl, 3-methyl-3-pentyl, 2-methyl-3-pentyl,2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, and the like. As used here, “aryl” refers to a5- or 6-membered heterocyclic, oxyheterocyclic, or thioheterocyclicring, including an arylalkyl, arylalkyloxy, arylalkylthio ring, and thelike.

In some embodiments, the ligand is replaced by a coordinating solventmolecule (i.e., a solvent molecule with a donor atom) upon dissociation.In an embodiment, a ligand does not remain coordinated to the metal upondissociating the metal salt, e.g., in presence of a solvent such aswater.

In an embodiment, the metal salt includes a metal as a metal cation suchthat the vapor deposition composition efficiently provides for formationof deposit 20 on substrate 4. The metal salt can have a low meltingpoint and sufficient thermal stability to dissociate and release themetal cation and the reducing anion in some embodiments.

According to an embodiment, the metal salt includes metal ion (M′)complexed with neutral ligand (L) or a combination of neutral ligand (L)and negatively charged ligand (Y). In an embodiment, a combination ofneutral ligands L and negatively charged ligands Y are included suchthat a total negative charge of the total number of negatively chargedligands Y is less than or equal to an oxidation state of metal ion M⁺.The ligands (L or Y) can be weakly coordinating to facilitate theirremoval during dissociation of the primary reagent metal salt to providemetal cation M⁺ and reducing anion (A−). Here, the ligands (L, Y)provide reducing anion A− upon dissociating the metal salt. Counteranions (X) can be weakly coordinating to reduce a melting point and toprevent direct binding to metal ion M⁺. The liquid metal thus provides ametal source for deposit 20. At activating catalyst 28, metal ion M⁺ isreduced to a metallic state to produce metal M of deposit 20. Electronsfor reducing metal ion M⁺ can be provided by substrate 4 or reducinganion A− from the ligands (L or Y) or counter anion X.

Exemplary metals M (of metal salt) that correspond to metal cation M⁺include copper, zinc, cadmium, nickel, cobalt, manganese, iron,chromium, tin, lead, bismuth, antimony, selenium, tellurium, thallium,silver, gold, platinum, palladium, rhodium, ruthenium, iridium, osmium,rhenium, aluminium, gallium, indium, silicium, germanium, beryllium,magnesium, titanium, zirconium, hafnium, molybdenum, tungsten, scandium,yttrium, lanthanum, cerium, praseodymium, neodymium, promethium,samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium,thulium, ytterbium, lutetium, thorium, uranium, plutonium lithium, andthe like.

Exemplary ligands L include a neutral ligand such as acetonitrile (AN),propionitrile, butyronitrile, isobutyronitrile, acrylonitrile,2-hydroxycyanoethane, phenylacetonitrile, benzonitrile benzylnitrile,dimethylformamide (DMF), acetamide, N,N-dimethylacetamide, formamide,N-methylformamide, N-methylacetamide, dimethylsulfoxide (DMSO),dimethylsulfone (DMSO₂), hexamethylphosphoramide (HMPA),N-methylpyrrolidone (NMP), pyridine (Py), morpholine, tetrahydrofuran(THF), diethyl ether, dimethoxyethane (DME, monoglyme),bis(2-methoxyethyl) ether (diglyme), triglyme, tetraglyme, pentaglyme,hexaglyme, 1,4-dioxane, methanol, ethanol, propanol, butanol,ethyleneglycol, polyethyleneglycol, water, trialkylphosphine oxides,triarylphosphine oxides, trialkylphosphate, pyrazole, 3-alkylpyrazoles,5-alkylpyrazoles, 3,5-dimethylpyrazole, imidazole, 1-alkylimidazoles,1,2-dimethylimidazole, 2-imidazolidinone, thiabendazole, ammonia,tetramethylenesulfoxide (TMSO), urea, N,N,N′,N′-tetramethylurea (TMU),thiourea, lactams, hydroxypyridines, 2-pyridone, pyridine-N-oxide,picoline-N-oxide, 2,6-lutidine, 2,6-lutidine N-oxide, pyrazine,pyrazine-N-oxide, 1,4-dithiane monosulfoxide, 2,2′-bipyridine (bipy),1,10-phenanthroline (phen), 2,6,2′,2″-terpyridine (terpy),ethylenediamine, diethylenetriamine, 1,2,3-triaminopropane, cyclam,crown ethers and thiacrown ethers, and the like.

Exemplary negatively charged ligands Y include chloride, bromide,iodide, thiocyanate, formate, acetate, trifluoroacetate, propionate,butyrate, pentanoate, hexanoate, benzoate, glycolate,heptafluorobutanate, alkylsulfate, octylsulfate, dodecylsulfate,triflate, methanesulfonate, nitrate, dicyanamide, tricyanomethanide,bis(trifluoromethylsulfonyl)imide (bistriflimide) orbis(perfluoroalkylsulfonyl)imide, dimethylphosphate, diethylphosphate,dialkylphosphate, saccharinate, acesulfamate tosylate, and the like.

Exemplary counter anions X include hexafluorophosphate,tetrafluoroborate, chloride, bromide, iodide acetate, trifluoroacetate,triflate, methanesulfonate, nitrate, perchlorate, dicyanamide,tricyanomethanide, bis(trifluoroalkylsulfonyl)imide,bis(trifluoromethylsulfonyl)imide (bistriflimide),bis(perfluoroalkylsulfonyl)imide, alkyltrifluoroborate,dimethylphosphate, diethylphosphate, dialkylphosphatetetrachloroaluminate, tetrachlorogallate, tetrachloroindate,tetrachloroferrate, hexachloroarsenate, hexachlorantimonate(VI),hexachlorotantalate, hexachloroniobate, and the like.

In an embodiment, a formula of the metal salt is M⁺LYX, where M⁺ is themetal ion metal; L is the neutral ligand; Y is the negatively chargedligand; and X is the counter anion. In some embodiments, e.g. when M+has a charge of +1, Y is not present and the general formula of suchliquid metal salt is M⁺LX.

In a particular embodiment, the liquid metal salt includesmetal-containing liquid metal salts that include a liquid metal salt offormula [M⁺L]X, wherein [M⁺L] is a cation complex wherein M⁺ is themetal ion such as a cation of copper, zinc, cadmium, nickel, cobalt,manganese, iron, chromium, tin, lead, bismuth, antimony, selenium,tellurium, thallium, silver, gold, platinum, palladium, rhodium,ruthenium, iridium, osmium, rhenium, aluminum, gallium, indium, silicon,germanium, beryllium, magnesium, titanium, zirconium, hafnium,molybdenum, tungsten, scandium, yttrium, lanthanum, cerium,praseodymium, neodymium, promethium, samarium, europium, gadolinium,terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium,thorium, uranium, plutonium, lithium, and the like; L is the neutralligand such as acetonitrile (AN), propionitrile, butyronitrile,isobutyronitrile, acrylonitrile, 2-hydroxycyanoethane,phenylacetonitrile, benzonitrile benzylnitrile, dimethylformamide (DMF),acetamide, N,N-dimethylacetamide, formamide, N-methylformamide,N-methylacetamide, dimethylsulfoxide (DMSO), dimethylsulfone (DMSO₂),hexamethylphosphoramide (HMPA), N-methylpyrrolidone (NMP), pyridine(Py), morpholine, tetrahydrofuran (THF), diethyl ether, dimethoxyethane(DME, monoglyme), bis(2-methoxyethyl) ether (diglyme), triglyme,tetraglyme, pentaglyme, hexaglyme, 1,4-dioxane, methanol, ethanol,propanol, butanol, ethyleneglycol, polyethyleneglycol, water,trialkylphosphine oxides, triarylphosphine oxides, trialkylphosphate,pyrazole, 3-alkylpyrazoles, 5-alkylpyrazoles, 3,5-dimethylpyrazole,imidazole, 1-alkylimidazoles, 1,2-dimethylimidazole, 2-imidazolidinone,thiabendazole, ammonia, alkylamines, tetramethylenesulfoxide (TMSO),urea, N,N,N′,N′-tetramethylurea (TMU), thiourea, lactams,hydroxypyridines, 2-pyridone, pyridine-N-oxide, picoline-N-oxide,2,6-lutidine, 2,6-lutidine N-oxide, pyrazine, pyrazine-N-oxide,1,4-dithiane monosulfoxide, 2,2′-bipyridine (bipy), 1,10-phenanthroline(phen), 2,6,2′,2″-terpyridine (terpy), ethylenediamine,diethylenetriamine, 1,2,3-triaminopropane, cyclam, crown ethers andthiacrown ethers, and the like; and X is the counter anion such ashexafluorophosphate, tetrafluoroborate, chloride, bromide, iodideacetate, trifluoroacetate, triflate, methanesulfonate, nitrate,perchlorate, dicyanamide, tricyanomethanide, bis(trifluoroalkylsulfonyl)imide, bis(trifluoromethylsulfonyl)imide (bistriflimide),bis(perfluoroalkylsulfonyl)imide, alkyltrifluoroborate,dimethylphosphate, diethylphosphate, dialkylphosphatetetrachloroaluminate, tetrachlorogallate, tetrachloroindate,tetrachloroferrate, hexachloroarsenate, hexachlorantimonate(VI),hexachlorotantalate, hexachloroniobate, and the like.

In a particular embodiment, the liquid metal salt includes negativelycharged ligand Y and has a formula [M⁺LY]X, wherein [M⁺LY] is a cationcomplex; X is the counter anion; M⁺ is the metal cation of a metal suchas copper, zinc, cadmium, nickel, cobalt, manganese, iron, chromium,tin, lead, bismuth, antimony, selenium, tellurium, thallium, silver,gold, platinum, palladium, rhodium, ruthenium, iridium, osmium, rhenium,aluminum, gallium, indium, silicon, germanium, beryllium, magnesium,titanium, zirconium, hafnium, molybdenum, tungsten, scandium, yttrium,lanthanum, cerium, praseodymium, neodymium, promethium, samarium,europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,ytterbium, lutetium, thorium, uranium, plutonium, lithium, and the like;L is the neutral ligand such as acetonitrile (AN), propionitrile,butyronitrile, isobutyronitrile, acrylonitrile, 2-hydroxycyanoethane,phenylacetonitrile, benzonitrile benzylnitrile, dimethylformamide (DMF),acetamide, N,N-dimethylacetamide, formamide, N-methylformamide,N-methylacetamide, dimethylsulfoxide (DMSO), dimethylsulfone (DMSO₂),hexamethylphosphoramide (HMPA), N-methylpyrrolidone (NMP), pyridine(Py), morpholine, tetrahydrofuran (THF), diethyl ether, dimethoxyethane(DME, monoglyme), bis(2-methoxyethyl) ether (diglyme), triglyme,tetraglyme, pentaglyme, hexaglyme, 1,4-dioxane, methanol, ethanol,propanol, butanol, ethyleneglycol, polyethyleneglycol, water,trialkylphosphine oxides, triarylphosphine oxides, trialkylphosphate,pyrazole, 3-alkylpyrazoles, 5-alkylpyrazoles, 3,5-dimethylpyrazole,imidazole, 1-alkylimidazoles, 1,2-dimethylimidazole, 2-imidazolidinone,thiabendazole, ammonia, alkylamines, tetramethylenesulfoxide (TMSO),urea, N,N,N′,N′-tetramethylurea (TMU), thiourea, lactams,hydroxypyridines, 2-pyridone, pyridine-N-oxide, picoline-N-oxide,2,6-lutidine, 2,6-lutidine N-oxide, pyrazine, pyrazine-N-oxide,1,4-dithiane monosulfoxide, 2,2′-bipyridine (bipy), 1,10-phenanthroline(phen), 2,6,2′,2″-terpyridine (terpy), ethylenediamine,diethylenetriamine, 1,2,3-triaminopropane, cyclam, crown ethers,thiacrown ethers, and the like; Y the negative ligand such as chloride,bromide, iodide, thiocyanate, formate, acetate, trifluoroacetate,propionate, butyrate, pentanoate, hexanoate, benzoate, glycolate,heptafluorobutanate, alkylsulfate, octylsulfate, dodecylsulfate,triflate, methanesulfonate, nitrate, dicyanamide, tricyanomethanide,bis(trifluoromethyl sulfonyl)imide (bistriflimide) orbis(perfluoroalkylsulfonyl)imide, dimethylphosphate, diethylphosphate,dialkylphosphate, saccharinate, acesulfamate, tosylate, and the like;and X is the counter anion such as hexafluorophosphate,tetrafluoroborate, chloride, bromide, iodide acetate, trifluoroacetate,triflate, methanesulfonate, nitrate, perchlorate, dicyanamide,tricyanomethanide, bis(trifluoroalkylsulfonyl)imide,bis(trifluoromethylsulfonyl)imide (bistriflimide),bis(perfluoralkylsulfonyl)imide, methyltri fluoroborate,alkyltrifluoroborate, diethylphosphate, dialkylphosphate,tetrachloroaluminate, tetrachlorogallate, tetrachloroindate,tetrachloroferrate, hexachloroarsenate, hexachlorantimonate(VI),hexachlorotantalate and hexachloroniobate, and the like.

Exemplary metal salts include copper(I) tetrakis(acetonitrile),bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(methylimidazole),bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(butylimidazole),bis(trifluoromethylsulfonyl)imide, copper(I) bis(2,2′-bipyridine),bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(pyridine),bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(3-picoline),bis(trifluoromethylsulfonyl)imide, copper(I) tetrakis(benzonitrile),bis(trifluoromethylsulfonyl)imide, zinc(II)bis(trifluoromethylsulfonyl)imide hexahydrate, silver(I)tetrakis(acetonitrile) bis(trifluoromethylsulfonyl)imide, silver(I)tris(acetonitrile) bis(trifluoromethylsulfonyl)imide, silver(I)(acetonitrile), bis(trifluoromethylsulfonyl)imide, silver(I)bis(acetonitrile), bis(trifluoromethylsulfonyl)imide,silver(I)mono(acetonitrile), bis(trifluoromethylsulfonyl)imide,copper(I) tetrakis(methylimidazole), trifluoromethanesulfonate,silver(I) tetrakis(acetonitrile), bis(trifluoromethylsulfonyl)imide,silver(I) tris(acetonitrile), bis(trifluoromethylsulfonyl)imide,silver(I) (acetonitrile), silver(I) bis(acetonitrile),bis(trifluoromethylsulfonyl)imide and silver(I)mono(acetonitrile),bis(trifluoromethylsulfonyl)imide, and the like.

The metal salt can be prepared synthetically by a method known in theart or obtained from a commercial source.

According to an embodiment, etch void 6, coating 22, and deposit 20 areformed by etching substrate 4 or depositing deposit 20 on substrate 4.In an embodiment, a process for etching or depositing includesmetal-assisted chemical etching described or metal-assisted depositiondescribed in Hildreth et al., “Effect of Catalyst Shape and EtchantComposition on Etching Direction in Metal-Assisted Chemical Etching ofSilicon to Fabricate 3D Nanostructures,” ACS Nano 3, 4033 (2009);Hildreth et al., “3D Out-of-Plane Rotational Etching with PinnedCatalysts in Metal-Assisted Chemical Etching of Silicon,” Adv. Funct.Mater. 21, 3119 (2011); Hildreth et al., “Combining Electroless Fillingwith Metal-Assisted Chemical Etching to Fabricate 3D Metallic Structureswith Nanoscale Resolutions,” ECS Solid State Lett. 2, P30 (2013); orHildreth et al., “Vapor Phase Metal-Assisted Chemical Etching ofSilicon,” Adv. Funct. Mater. 24, 3827 (2014), the disclosure of each ofwhich is incorporated herein by reference in its entirety.

In an embodiment, coating 22 having a uniform density gradient iscontrollably formed in substrate 4. Here, a plurality of activatingcatalysts 28 that includes, e.g., different activating catalyst 28 withdifferent sizes of activating catalyst 28 are used to etch a pluralityof different depths in substrate 4. Etching can occur in a single etchstep or a selected number of steps. Activating catalyst 28 (e.g., Ag,Au, Pt, or Pd) is disposed on substrate 4 (e.g., silicon), and substrate4 with activating catalyst 28 disposed thereon is immersed in liquidmedium 30, e.g., a composition that includes an activatable etchant(e.g., HF) and etchant oxidizer (e.g., H₂O₂). Metal of activatingcatalyst 28 is a catalyst that reduces the etchant oxidizer. Withoutwishing to be bound by theory, it is believed that reducing the etchantoxidizer injects holes (h⁺) into substrate 4 to produce a hole (h⁺)-richregion in substrate 4 proximate to activating catalyst 28. This hole(h⁺) rich region is oxidized by the activatable etchant (e.g., HF) toform etchant product 32 (e.g., SiF₆ ²⁻, H₂SiF₆, and the like). Etchantproduct can be soluble and removed by solvating etchant product 32 inliquid medium 30 or in a rinse composition, e.g., distilled water oralcohol. Formation of additional etchant product 32 proceeds asactivating catalyst 28 moves and propagates in substrate 4. In thismanner, the motion of activating catalyst 28 provides high featureresolution of etch void 6 even when etch void 6 has an ultra-high aspectratio.

Thus, it is contemplated that the activatable etchant may not etchsubstrate 4 (e.g., undamaged silicon) at an appreciable rate. For thispurpose, activating catalysts 28 catalyzes reduction of etchant oxidizer(e.g., H₂O₂) to consume electrons from substrate 4 and injects holes(h⁺) into a valance band of substrate 4. As a result, in a particularembodiment, such a process creates a hole (h⁺) rich region of siliconsurrounding activating catalyst 28 that is oxidized by HF to formsoluble SiF₆ ²⁻ and H₂SiF₆ with the reaction continuing as activatingcatalyst 28 is pulled into substrate 4 by van der Waals or electrostaticforces. Without wishing to be bound by theory, it is believed thatactivating catalyst 28 produces a localized, traveling galvanic etchingreaction to produce one-dimensional, two-dimensional, orthree-dimensional nanostructures or microstructures in substrate 4.Accordingly, since activatable etchant may not etch substrate 4 and isappreciable rate, activating catalyst 28 activates the activatableetchant to etch substrate 4 in a presence of the etchant oxidizers.

In a particular embodiment, the process includes etching substrate 4wherein activating catalyst 28 (e.g., silver) is deposited ontosubstrate 4 (e.g., silicon) and contacted by liquid medium 30 thatincludes the activatable etchant (e.g., hydrofluoric acid) and etchantoxidizer (e.g., hydrogen peroxide) to initiate redox reactions thatinclude cathodic and anodic redox reactions as described in Hildreth etal., U.S. Pat. No. 8,278,191, granted Oct. 2, 2012, the disclosure ofwhich is incorporated herein in its entirety.

In an embodiment, a shown in FIGS. 12A, 12B, and 12C, a process forforming coating 22 includes disposing activating catalyst 28 onsubstrate 4, introducing the activatable etchant, introducing theetchant oxidizer, and performing an oxidation-reduction reaction betweensubstrate 4, the activatable etchant, and the etchant oxidizer in apresence of activating catalyst 28 such that the oxidation-reductionreaction occurs in presence of liquid medium 30. Liquid medium 30includes the activatable etchant and the etchant oxidizer. The processfurther includes forming etchant product 32 (that includes a pluralityof atoms from substrate 4), removing a portion of etchant product 32from substrate 4 to form undercut 34 interposed between activatingcatalyst 28 and substrate 4, and forming a dendritic vein (not shown inFIG. 12A, 12B, or 12C but see FIGS. 7 and 8) in substrate 4 to formcoating 20 (not shown). The dendritic veins are anisotropically disposedin the coating. As used herein, “anisotropically” refers to an absenceof a point, line, or plane of symmetry of the dendritic veins such thatetch voids 6 are not substantially identical in an arrangement disposalof etch voids 6 in substrate 4, as shown in FIGS. 7 and 8.

In an embodiment, as shown in FIG. 13, a plurality of differentactivating catalysts, i.e., first activating catalyst 36, secondactivating catalyst 38, third activating catalyst 40, and the like, aredisposed on substrate 4 to produce etch voids 6 having a plurality ofdifferent depths (respectively, first depth d1, second depth d2, thirddepth d3, and the like) in substrate 4. In a particular embodiment,first activating catalyst 36, second activating catalyst 38, and thirdactivating catalyst 40 have a different rate for forming etch voids 6.In a specific embodiment, first activating catalyst 36, secondactivating catalyst 38, and third activating catalyst 40 independentlyinclude Ag, Au, or Pt that respectively have an etch rate of 5 nm/sec(Ag), 50 nm/sec (Au), and 1,000 nm/sec (Pt) in silicon.

In an embodiment, as shown in FIG. 14, a plurality of activatingcatalysts, i.e., first activating catalyst 43, second activatingcatalyst 44, third activating catalyst 46, and the like, are disposed onsubstrate 4 to produce etch voids 6. Here, first activating catalyst 43,second activating catalyst 44, and third activating catalyst 46 havedifferent sized, respectively shown as first size S1, second size S2,and third size S3, from smallest to largest size. Size here can be alargest cross-sectional linear dimension or area. By virtue of differingsize, first activating catalyst 43, second activating catalyst 44, andthird activating catalyst 46 produce etch voids 6 having a plurality ofwidths, respectively first width W1, second width W2, and third widthW3. It is contemplated that first activating catalyst 43 having asmaller size (first size S1) produces etch void 6 that has a greaterdepth in substrate four than etch void 6 formed by second activatingcatalyst 44 or third activating catalyst 46 that have a larger size thanfirst activating catalyst 43. Without wishing to be bound by theory, itis believed that an etch rate of activating catalyst 28 (e.g., firstactivating catalyst 43, second activating catalyst 44, third activatingcatalyst 46) varies inversely with size S (i.e., 1/S³).

According to an embodiment, with reference to FIG. 15, coating 22 isformed from substrate 4 from interaction of the activatable etchant andetchant oxidizer with first activating catalysts (36A, 36B, 36C), secondactivating catalysts (38A, 38B, 38C), and third activating catalyst(40A, 40B, 40C) having different identities (i.e., metal composition)and sizes to produce a plurality of etch voids (6A, 6B, 6C, 6D, 6E, 6F,6G, 6H, 6I) having different shapes and depths. Here, a density gradientis etched into substrate 4 by selectively disposing activating catalysts(36A, 36B, 36C, 38A, 38B, 38C, 40A, 40B, 40C) on substrate 4 to etch theplurality of etch voids (6A, 6B, 6C, 6D, 6E, 6F, 6G, 6H, 6I). As such, adensity gradient in a volume of a material of substrate 4 is createdactivating catalysts (36A, 36B, 36C, 38A, 38B, 38C, 40A, 40B, 40C) incombination with the activatable etchand and etchant oxidizer etch adifferent depth into substrate 4. That is, coating 22 (top portion ofarticle 2 above fudicial line 3) is heavily etched and very porous(porosity not shown in FIG. 15—but see FIGS. 7 and 8) with andincreasing density as number density of activating catalysts (36A, 36B,36C, 38A, 38B, 38C, 40A, 40B, 40C) decreases with depth into substrate4. Here, coating 22 nominally terminates at fudicial line 3 (which wouldbe a surface in three-dimensional space). Also, larger sized activatingcatalysts (e.g., 36C, 38C, 40C) have a slower etch rate than small-sizedactivating catalysts (e.g., 36A, 38A, 40A). It is contemplated thatdifferent activating catalysts (e.g., Ag compared with Pt) or activatingcatalysts having different sizes produce a density gradient within insubstrate 4.

With reference again to FIGS. 7 and 8, activating catalyst 28 moves inin a three-dimensional volume in substrate 4 as substrate 4 is etched.This motion of activating catalyst 28 in the three-dimensional volume iscontrolled in an embodiment, e.g., by application of an externalelectric field. According to an embodiment, etching substrate 4 includesdynamically changing when activating catalyst 28 etches in a verticaldirection (relative to a surface of substrate 4 from which activatingcatalyst 28 was disposed on substrate 4) to remove comparatively littlesubstrate material per unit depth of substrate 4. Further, etchingsubstrate 4 includes dynamically changing when activating catalyst 28and etches in lateral direction (relative to a surface of substrate 4from which activating catalyst 28 was disposed on substrate 4) to removecomparatively more material per unit depth of substrate 4. In someembodiments, these three features are used in combination orindependently such that a plurality of different activating catalystshaving different sizes that move along a plurality of different etchingpaths produces a uniform gradient in coating 22 as shown in FIGS. 7 and8.

In an embodiment, etching substrate 4 produces gas (e.g., H₂) that canbe disposed initially as bubbles in substrate 4. Certain bubbles of thegas can interconnect within the forming coating 22. In this manner, aplurality of dendritic veins is anisotropically disposed in coating 22.Further, evolution of the gas produces a microporous layer of thematerial of substrate 4 as coating 22 is formed from the same materialthat composes substrate 4. Accordingly, a gradient in a density of avolume of the microporous layer is produced by virtue of a plurality ofdifferent activating catalysts having different sizes and compositionproducing the microporous layer with a terminal depth of the pluralityof the activating catalysts being different in various portions ofcoating 22. In a certain embodiment, the process includes forming thegradient in the density of the volume of coating 22. Additionally, theprocess includes controlling an index of refraction of the coating toproduce the coating with a uniform gradient in the index. Moreover, theprocess can include changing a condition to affect a condition (e.g.,temperature, concentration of etchant oxidizer or activatable etchant,and the like) of coating 22. The redox reaction can be terminatedcontrollably by quenching etching of substrate 4 (e.g., by removingetchant oxidizer, introducing a catalyst poisoner, and the like). Insome embodiments, the redox reaction terminates by reactingsubstantially all of a limiting reactant (e.g., etchant oxidizer oractivatable etchant). According to an embodiment, the process includesremoving activating catalyst 28 from contact with substrate 4 to producearticle 2. In a certain embodiment, the process includes washing article2 to remove etchant product 32 to expose etch void 6, e.g., dendriticveins 24.

In an embodiment, a reflectivity of coating 22 is controlled to be acertain value or to have a range of values across a surface of coating22.

With regard to removing activating catalyst 28 from etch void 6, in anembodiment, after etch void 6 is formed (or when activating catalyst 28is left as a residual material on a surface of coating 22), activatingcatalyst 28 (e.g., Pt) remains in etch void 6, which may be open orclosed cell pores, dendritic vein 24, or open and exposed etch void 6.Some of activating catalysts 28 may be distributed throughout coating22. Such activating catalyst 28 can be removed from coating 22 after theformation process. A leaching process can be used to remove at least aportion or substantially all of activating catalyst 28 from etch voids6. As used herein, “substantially all” means having a total amount ofactivating catalyst 28 in coating 22 of article 2 of less than about 5wt. %, specifically less than or equal to about 4 wt. %, still morespecifically less than or equal to about 0. Wwt. %, based on the weightof activating catalyst 28 per unit volume of leached region of article2.

In one embodiment, the polycrystalline diamond may be leached using aleaching agent and process such as those described more fully in, forexample, U.S. Pat. No. 5,127,923 and U.S. Pat. No. 4,224,380, thedisclosure of each of which patent is incorporated herein by referencein its entirety.

For example, aqua regia, which is a mixture of concentrated nitric acid(HNO₃) and concentrated hydrochloric acid (HCl), in any effectiveproportion such as, for example, in a 1:3 (v/v) ratio, may be used to atleast remove substantially all activating catalyst 28 from etch voids 6.Alternatively, boiling hydrochloric acid (HCl) may be used as theleaching agent. In an exemplary embodiment, a useful leaching agent ishydrochloric acid (HCl) heated to a temperature of greater than 110° C.,which may be provided in contact with article 2 for 5 minutes in to1,000 hours or even greater, depending upon the size of article 2, andthe extent of leaching desired in coating 22. In some embodiments anorganic aqua regia is used to remove activating catalyst 28. Anexemplary organic regia is described in U.S. patent application Ser. No.13/820,358, which is incorporated by reference in its entirety.

In an embodiment, leaching comprises immersing article 22 (or a portionthereof, e.g., coating 22) in a leaching agent (e.g., hydrochloric acid,nitric acid, or a combination thereof) at a temperature effective toremove activating catalyst 28, e.g., at a temperature greater than orequal to 20° C. After leaching the activating catalyst 28 from coating22, article 2 may be free of substantially all activating catalyst 28used to catalyze formation of etch voids 6.

According to an embodiment, coating 22 is formed by an electrochemicalprocess. Here, a process for forming a coating includes disposingactivating catalyst 28 on substrate 4, introducing the activatableetchant, subjecting activating catalyst 28 and the activatable etchantto an electric potential, and performing an electrochemical reactionbetween substrate 4 and the activatable etchant in a presence ofactivating catalyst 28 and the electric potential. The electrochemicalreaction occurs in liquid medium 30 that includes the activatableetchant and the etchant oxidizer. The process further includes formingetchant product 32 that includes a plurality of atoms from substrate 4,removing a portion of etchant product 32 from substrate 4, and forming aplurality of dendritic veins 24 in substrate 4 to form coating 22. Theplurality of dendritic veins 24 are anisotropically disposed in coating22. The electric potential has a magnitude effective to reduceactivatable etchant at activating catalyst 28 and to form etchantproduct 32 from the activatable etchant and substrate 4. In anembodiment, the process includes removing etchant product 32 fromdendritic veins 24. In some embodiments, etchant product 32 ismaintained in etch voids 6 and not removed.

According to an embodiment, a controllable density gradient is formed ina substrate (e.g., silicon) using a liquid composition having theactivatable etchant in presence of activating catalyst 28 on substrate4. The density gradient can be controlled by adjusting a material ofactivating catalyst 28; adjusting a size of activating catalyst 28;changing a path of motion of activating catalyst 28 and substrate 4;changing components in liquid medium 30; and the like. Surface etchingcan be enhanced by adjusting an identity of the activatable etchant oretchant oxidizer. It is contemplated that etch void 6 can have aone-dimensional, two-dimensional, or three-dimensional structure insubstrate 4 such as silicon or other III-IV-V semiconductors usingpatterned or deposited activating catalysts 28 on substrate 4 followedby exposure to liquid medium 30 that includes the activatable etchant(e.g., HF) or oxidizing agent such as H₂O₂. It is contemplated thatetching path (i.e., motion of activating catalyst in substrate 40) iscontrolled by selection of the shape of activating catalyst 28;application of an external fields (e.g., a magnetic field, electricfield, or combination thereof); adjustment of concentration ofactivatable etchant, etchant oxidizer, or combination thereof (e.g., HFor H₂O₂); and the like. Resolution during the etching and of etch void 6is controlled by adjusting activating catalysts 28 identity (i.e.,metallic species), shape, composition, and the like; adjustingconcentration of the activatable etchant; adjusting concentration of theetchant oxidizer; and the like.

In an embodiment, article 2 includes coating 22, or and coating 22 is ananti-reflective coating. Such antireflective coatings can be implementedin a detector for microwave frequencies, e.g., a detector in atelescope. Although conventional techniques use dicing or deep reactiveion etching that can be slow, expensive, or create one or two discretedensities in a substrate, the process herein surprisingly providecontinuous density gradients of an arbitrary gradient and depth at lowmonetary and time cost. Advantageously, processes herein etch servicesthat are later, a regular, curved, and the like without limitation tosurface curvature. As such, the processes herein can etch a vast varietyof substrates to form lenses (planar and curved), containers, throughholes, blind holes, tailorable apertures, undulating surface contouring,and the like.

In an embodiment, etching substrate 4 is accomplished using a vaporcomposition that comprises the activatable etchant. With reference toFIGS. 16A, 16B, 16C, and 16D, a process for etching substrate 4 includesdisposing activating catalyst 28 on substrate 4; providing vaporcomposition 42 comprising an etchant oxidizer, an activatable etchant,or a combination thereof to substrate 4, activating catalyst 28, or acombination thereof; contacting activating catalyst 28 with the etchantoxidizer, contacting substrate 4 with the activatable etchant;performing an oxidation-reduction reaction between substrate 4, theactivatable etchant, and the etchant oxidizer in a presence ofactivating catalyst 28 and vapor composition 42; forming etchant product32 that includes a plurality of atoms from substrate 4; and removingetchant product 32 from substrate 4 to etch substrate 4. Duringproviding vapor composition 42 to substrate 4 or activating catalyst 28,vapor composition 42 and Sorbs two substrate 4 or activating catalyst 28to form etchant adsorbent 50. Etchant adsorbent 50 includes the etchantoxidizer and activatable etchant, e.g., in a thin layer such thatetchant product 32 is formed efficiently. In this manner, etchantproduct 32 can be formed from a relatively low vapor pressure liquidmedium 30 so that although vapor composition 42 may not have a highnumber density, etch adsorbent 50 includes a high number density of theactivatable etchant or etchant oxidizer. Furthermore, in an embodiment,vapor composition 42 can be continually provided to substrate 4 oractivating catalyst 28. In some embodiments, vapor composition 42 ismodulated to provide a temporally varying amount of the activatableetchant or etchant oxidizer two substrate 4 or activating catalyst 28.According to an embodiment, a plurality of liquid media 30 is present inseparate containers such that different or redundant streams of vaporcomposition 42 can be provided to substrate 4 or activating catalyst 28.

As shown in FIGS. 16B and 16C, as etchant product 32 is produced byinteraction of components of etch adsorbent 50 with activating catalyst28 and substrate 4, undercut 34 is made in substrate 4 by removal ofetchant product 32 from substrate 4. In this manner, atoms fromsubstrate 4 are etched away by components of etch adsorbent 50 inpresence of substrate 4 and activating catalyst 28. FIG. 16 D showsaccumulation of removal of atoms of substrate 4 such that etch void sixis produced in substrate four by cumulative removal of etch product 32.

In an embodiment, the process further includes adjusting a position ofactivating catalyst 28 in substrate 4, e.g., by using an external fieldsuch as a magnetic field or an electric field as etchant product 32 isremoved. In some embodiments, a position of activating catalyst 28 asetch void 6 is formed is controlled by physically altering a position ofactivating catalyst 28 such as by tethering a portion of activatingcatalyst 28 to external portion of substrate 4 or an exterior memberthat may or may not be attached to substrate 4. In this manner, theexterior member can serve as anchor to control the position ofactivating catalyst 28 or a path of travel of activating catalyst 28 insubstrate 4 as etch void 6 is formed. As a result of controlling aposition of activating catalyst 28 during etching of substrate 4, ashape of etch void 6 corresponds to a cumulative position of activatingcatalyst 28 in substrate 6. The process can further include controllinga rate of forming etch product 32. The rate can include isolatingactivating catalyst 28 from the etchant oxidizer, substrate 4 fromactivatable etchant 28, or a combination thereof. In an embodiment,isolating is conducted intermittently. As used herein, “intermittently”refers to stopping or ceasing for a time or alternately ceasing andbeginning again. In some embodiments, controlling the rate includeschanging a rate of formation of etch product 32. Alternatively,controlling the rate can include maintaining the rate of formation ofetch product 32 at a substantially constant rate.

It is contemplated that, in this process, etch void 6 is aone-dimensional etch void, a two-dimensional etch void, athree-dimensional etch void, or a combination comprising at least one ofthe foregoing etch voids in substrate 4 as a result of adjusting aposition of activating catalyst 28 in substrate 4. In an embodiment, theprocess also includes forming dendritic vein 24 in substrate 4 to formcoating 22 such that dendritic vein 24 is anisotropically disposed incoating 22. Substrate 4 can include a plurality of etch voids 6 formedin substrate 4 of a single etch void 6. For the plurality of etch voids6, substrate 4 can have a gradient in a density of a volume of substrate4 due to a presence of the plurality of etch voids 6. Here, etch voids 6can have an arbitrary shape by virtue of controlling a position ofactivating catalyst 28 during etching using the vapor composition. In anembodiment, substrate 4 includes the plurality of etch voids 6 arrangedsuch that substrate 4 has a uniform density of a volume of substrate 4due to a presence of the plurality of etch voids 6.

In some embodiments, activating catalyst 28 is disposed on a surface ofsubstrate 4 in a selected pattern. In a particular embodiment,activating catalyst 28 is disposed on a surface of substrate four in arandom pattern. In a certain embodiment, activating catalyst 28 isdisposed on the surface of substrate 4 through a mask. Activatingcatalyst 28 can be disposed on the surface of substrate 4 by entrainingactivating catalyst 28 in a gas and delivering the gas containingactivating catalyst 28 to the surface of substrate 4. Alternatively,activating catalyst 28 can be disposed on the surface of substrate 4 bydisposing activating catalyst 28 and a liquid delivering the liquidcontaining activating catalyst 28 to the surface of substrate 4. Suchdelivery can be accomplished by spraying, spinning, knife-blading, andthe like the liquid containing activating catalyst 28 on the surface ofsubstrate 4. In an embodiment, substrate 4 can be immersed in liquidcontaining activating catalyst 28 whereby activating catalyst 28 adsorbsonto the surface of substrate 4. Thereafter, with activating catalyst 28disposed on the surface of substrate 4, substrate 4 can be exposed tothe liquid composition or vapor composition that contain the etchantoxidizer or activatable etchant. According to an embodiment, the etchantoxidizer is produced in the vapor composition from a liquid phase. In acertain embodiment, the activatable etchant is produced in the vaporcomposition from a liquid phase.

In one embodiment, activating catalyst 28, activatable etchant, etchantoxidizer, or combination thereof is disposed in a liquid or gas (e.g.liquid medium or a vapor composition) that contacts substrate 4 to formetch void 6 therein. Hence, in an embodiment, activating catalyst 28,activatable etchant, and etchant oxidizer contact substrate 4substantially simultaneously. In a further embodiment, activatingcatalyst 28, activatable etchant, or etchant oxidizer contact substrate4 at a different time with respect to contact of substrate 4 byactivating catalyst 28, activatable etchant, or etchant oxidizer.

In a certain embodiment, a first liquid medium includes the activatableetchant to provide a first vapor composition, and the second liquidmedium includes the etchant oxidizer such that the activatable etchantand etchant oxidizer independently are provided to substrate 4 oractivatable catalyst 28. Here, the first vapor composition and thesecond vapor composition can be synchronously provided to substrate 4 oractivating catalyst 28. Alternatively, the first vapor composition andsecond vapor composition can be asynchronously provided to substrate 4or activating catalyst 28. A combination of synchronous and asynchronousoperation of delivery of the first vapor composition in the second vaporcomposition to substrate 4 or activating catalyst 28 is contemplated.

It is contemplated vapor composition 42 etches substrate 4 to formarticle 2 having simple, complex, or combination thereofone-dimensional, two-dimensional or three-dimensional nano-sized ormicro-sized etch voids 6 in substrate 4 (e.g., silicon) a presence ofactivating catalysts 28 such as Ag, Au, Pt, Pd, and the like. Vaporcomposition 42 includes, in an embodiment, activatable etchant (e.g.,hydrofluoric acid (HF)) and etchant oxidizer (e.g., hydrogen peroxide(H₂O₂)). Activating catalyst 28 is deposited or patterned on a surfaceof the silicon substrate and exposed to HF and H₂O₂ vapor. Independentlychanging a partial pressure of HF and H₂O₂, activating catalyst shape,substrate temperature, and pressure provide control over the redoxreaction and etch rate of the silicon substrate. The etch rate, featureresolution, and etch path of activating catalyst 28 can be controlled toform one-dimensional, two-dimensional, or three-dimensional etch voids 6with an aspect ratio from 1:1 to greater than 500:1 and etch void 6resolution on the order of 100 nanometers (nm), specifically 20 nm, morespecifically 10 nm, and yet more specifically 1 nm. In an embodiment,vapor composition 42 provides high feature resolution andthree-dimensional nanofabrication for formation of article 2. Accordingto an embodiment, using the vapor composition to form etch void 6 insubstrate 4 to produce article 2 eliminates fluid flow and fluid-basedprocesses that reposition activating catalyst 28 on the surface ofsubstrate 4 that would otherwise degrade resolution and intendedmigration path of activating catalyst 28 and substrate four.Consequently, vapor composition 42 provides control over etching pathand etching length and reduces stop-lag periods, i.e., a time intervalbetween removal of activatable etchant 28 and when etching of substrate4 terminates.

In an embodiment, etching substrate 4 is accomplished using vaporcomposition vapor composition 42 to form etch voids 6 etch void 6 canhave a one-dimensional, two-dimensional, or three-dimensional structurein substrate 4 such as silicon or other III-IV-V semiconductors usingpatterned or deposited activating catalysts 28 on substrate 4 followedby exposure to vapor composition including the activatable etchant(e.g., HF) or oxidizing agent such as H₂O₂. It is contemplated thatetching path (i.e., motion of activating catalyst in substrate 40) iscontrolled by selection of the shape of activating catalyst 28;application of an external fields (e.g., a magnetic field, electricfield, or combination thereof); adjustment of concentration (e.g.,partial pressure) of activatable etchant, etchant oxidizer, orcombination thereof (e.g., HF or H₂O₂); and the like. Resolution of etchvoid 6 during the etching and of etch void 6 is controlled by adjustingactivating catalysts 28 identity (i.e., metallic species), shape,composition, and the like; adjusting concentration of the activatableetchant; adjusting concentration of the etchant oxidizer; adjustingtotal pressure of gases present; and the like. According to anembodiment, etching is controllable and can be started or stoppedquickly (e.g., within milliseconds) respectively by introducing orremoving the activatable etchant or etchant oxidizer. The activatableetchant or etchant oxidizer partial pressures can be controlledindependently by a gas or bubbler system (e.g., with a mass flowcontroller), concentrations of the activatable etchant or etchantoxidizer, temperature of a reservoir containing the activatable etchantor etchant oxidizer.

In some embodiments, the etching rate, etching time, etching featureresolution, etching path, or etch profile independently are controlleddynamically by changing the activatable etchant or etchant oxidizerpartial pressure, by adjusting a temperature of substrate 4; and thelike. Substrate 4 can be disposed in a chamber for etching. Substrate 4can be in a same chamber as the activatable etchant or etchant oxidizeror in a different chamber as the activatable etchant or etchantoxidizer. Further, substrate 4 can be oriented in a horizontal,vertical, upside-down (i.e., inverted), or at an arbitrary angle withrespect to earth's surface during etching.

Although conventional etching technology can be expensive with existingtechnology, etching substrate 4 with vapor composition 42 providesultra-fine resolutions (e.g., nanometer resolution) at aspect ratiosgreater than 500:1. Moreover, since vapor is used, fluid flow oversubstrate 4 does not occur such that the catalyst is not repositioned onthe surface of substrate 4 before etching starts. As a result, etchingwith vapor composition is repeatable and scalable to large substrates 4.Since vapor composition 42 eliminates fluid flow over substrate 4,entire wafers can be etched in a repeatable manner, and preciseintroduction or removal of vapor composition 42 provides control overetch time and etch depth. Additionally, since vapor composition 42eliminates fluid flow, a plurality of wafers can be processed in asingle chamber or a plurality of chambers. Drying substrate 4 afteretching may be skipped for use of vapor composition 42. Also, dense,high aspect ratio structures can be fabricated without collapsing undercapillary forces, and etching processes with vapor composition 42 issuitable for large volume manufacturing.

In some embodiment, a system for controlling (e.g., adjusting) atemperature of substrate 4 controls an etch rate of substrate 4.Controlling the temperature of substrate 4 can be used to control aphase of etch adsorbent 52. In an embodiment, the temperature iscontrolled during the etch period to control a parameter such as etchrate, feature resolution, etch structure, etch shape, and the like.

Etching removes material from substrate 4 and can also form a structuredelement (e.g., etch void 6, microporous layer, dendritic vein 24, andthe like) in substrate 4. Herein, etching substrate 4 includes etchingusing a condensed medium (e.g., liquid medium 30) or vapor phase (e.g.,vapor composition 42). In an embodiment, activating catalyst 28 is usedfor deposition of a material on substrate 4 to form deposit 20. Withreference to FIG. 17, a process for depositing a metal includesdisposing activating catalyst on substrate 4; contacting activatingcatalyst 28 with metal cation 64 from vapor deposition composition 60;contacting substrate 4 with reducing anion 66 from vapor depositioncomposition 60; performing an oxidation-reduction reaction between metalcation 64 and reducing anion 66 in a presence of activating catalyst 28on substrate 4; and forming metal 20 from metal cation 64 to depositmetal 20 on substrate 4. Here, vapor deposition composition 60 adsorbsonto substrate 4 as deposition adsorbent 52 that includes an appreciablenumber density of metal cation 64 and reducing anion 66 effective toform metal 20.

In some embodiments, the process for depositing metal 20 includesforming vapor deposition composition 60 by combining metal cation 64from a first source and reducing anion 66 from a second source andproviding vapor deposition composition 60 to substrate 4 and activatingcatalyst 28. Here, providing vapor deposition composition 60 tosubstrate 4 and activating catalyst 28 is for contacting activatingcatalyst 28 with metal cation 64 and contacting substrate 4 withreducing anion 66.

In some embodiments, the process for depositing metal 20 includesforming vapor deposition composition 60 that includes metal cation 64and reducing anion 66 and providing vapor deposition composition 60 tosubstrate 4 and activating catalyst 28. Here, providing vapor depositioncomposition 60 to substrate 4 and activating catalyst 28 is forcontacting activating catalyst 28 with metal cation 64 and contactingsubstrate 4 with reducing anion 66.

According to an embodiment, the process for depositing metal 20 includesfurther includes dissociating primary reagent 62 to form metal cation 64and reducing anion 66; forming metal cation 64 and reducing anion 66 ina liquid state (e.g., liquid medium 30) in response to dissociatingprimary reagent 62, and volatilizing metal cation 64, reducing anion 66,or a combination thereof to form vapor deposition composition 60.Primary reagent 62 can be disposed in a solvent to dissociate primaryagent 62. The process can include heating primary agent 62 to dissociateprimary agent 62 to provide metal cation 64 or reducing anion 66.

In an embodiment, the process also includes growing a structure on thesubstrate by forming the metal. The structure can include metal 20.Exemplary structures include protrusions, electrodes, mirrors, gratings,and the like.

In some embodiments, the process includes etching substrate 4 prior toforming metal 20 on substrate 4. With reference to FIGS. 18A, 18B, 18C,18D, 18E, and 18F, activating catalyst 28 is disposed on substrate 4(FIG. 18A), substrate 4 is subjected to etching to form etch void 6(FIG. 18B), metal 20 is formed on substrate 4 (FIG. 18C), formingsecondary substrate 54 (e.g., a semiconductor, metal, or polymer such asplastic) on metal 20 (by e.g., deposition) (FIG. 18D), removingsubstrate 4 from metal 20 (FIG. 18E, and removing activating catalyst 28from metal 20 to form an article having metal 20 (grown by using vapordeposition composition 60 on substrate 4 and activating catalyst 28)disposed on secondary substrate 54.

In an embodiment, the process includes etching substrate 4 anddepositing metal 20 on substrate 4 concurrently.

In a certain embodiment, the process for forming metal 20 on substrate 4includes etching substrate 4 by providing vapor composition 42 thatincludes the etchant oxidizer, activatable etchant, or a combinationthereof; contacting activating catalyst 28 with the etchant oxidizer,contacting substrate 4 with the activatable etchant; performing anoxidation-reduction reaction between substrate 4, the activatableetchant, and the etchant oxidizer in a presence of activating catalyst28 and vapor composition 42; forming etchant product 32 that includes aplurality of atoms from substrate 4; removing etchant product 32 fromsubstrate 4 to etch the substrate; and then forming metal 20 onsubstrate 4.

In an embodiment, the process for forming metal 20 on substrate 4includes etching substrate 4 by providing liquid medium 30 that includesthe activatable enchant, etchant oxidizer, or combination thereof;performing an oxidation-reduction reaction between substrate 4,activatable etchant, and etchant oxidizer in a presence of activatingcatalyst 28, wherein the oxidation-reduction reaction occurs in apresence of liquid medium 30; forming etchant product 32 that includes aplurality of atoms from substrate 4; and removing a portion of etchantproduct 32 from substrate 4 to etch substrate 4.

According to an embodiment, the process for forming metal 20 onsubstrate 4 further includes terminating forming metal 20, e.g., byquenching the growth of metal 20. Forming metal 20 also can includeforming a plurality of layers comprising metal 20 on substrate 4, e.g.,in a laminar structure or different layers on different portions ofsubstrate 4. In an embodiment that includes etching substrate 4 andforming metal 20 on substrate 4, the process can include filling a void(that may be the same or different than etch void 6) in substrate 4,e.g., with metal 20 formed by depositing metal 20 using vapor depositioncomposition 60 in combination with activating catalyst 28. In someembodiments, the void is different than etch void 6 and is a crackdisposed in substrate 4. It is contemplated that in certain embodimentsmetal cation 64 includes a plurality of different metal cations 64, andmetal 20 deposited on substrate 4 includes an alloy (e.g., Au—Pt, W—Rh,and the like. Further, primary agent 62 can include the metal salt,organometallic compound, and the like, or combination thereof.

In an embodiment, a system for depositing metal 20 on substrate 4includes activating catalyst 28 to deposit on substrate 4 and primaryreagent 62. Primary reagent 62 is provided to form metal cation 64 todeposit on substrate 4 as metal 20 and reducing anion 66 to provideelectrons to activating catalyst 28, metal cation 64, substrate 4, or acombination thereof. Here, primary reagent 62 forms metal cation 64 andreducing anion 66 in response to being subjected to a dissociatingcondition, e.g., heating, solvation, a kinetic or thermodynamic process(e.g., kinetic or thermodynamic equilibria), and the like.

Using vapor deposition composition 60 to form metal 20 on substrate 4provides a plurality of chemical precursors for low temperature chemicalvapor deposition (CVD) of metal 20. While conventional CVD processes forforming a metal may use an expensive organic precursor or involve aharsh chemical environment (e.g., high temperature, high-energy plasma,highly reactive reducing agents such as H₂), forming metal 20 onsubstrate 4 herein does not. Moreover, deposition processes hereinreduce the cost of metal 20 formation that forms at low temperatures(e.g., less than 100° C.) with inexpensive chemicals and in an absenceof high-energy plasmas. It is contemplated that deposition processesherein include a vapor phase electroless deposition to selectivelydeposit metal 20 on a plurality of different substrates 4 to form aconformal coating, to fill a via, to fabricate a one-dimensional,two-dimensional, or three-dimensional nanostructure on substrate 4.Further, metal 20 is disposed on substrate 4 in topside or backsidemetallization, e.g., for microelectronic devices, MicroElectroMechanicalSystems (MEMS), photonics, advanced communication devices, and the like.

It has surprisingly been found that vapor deposition composition 60 fromliquid medium 30 that includes, e.g., primary reagent 62 (e.g., a metalsalt (for metal cationic 64) and reducing anion 66 adsorbs as depositionadsorbent 52 on substrate 4. Deposition adsorbent 52 includes a thin,condensed layer including, e.g., metal cation 64, reducing anion 66, andwater in some embodiments. Metal ions 64 is reduced catalytically onactivating catalyst 28 to form solid metal 20. This process can be usedto fill vias and blind vias from a bottom up.

Using vapor deposition composition 60 that includes metal cation 64 toform metal 20 on substrate 4 as numerous advantages such as depositionoccurring at a low temperature, in a benign chemical environment, withchemical precursors that are cheap and readily available, and in areaction chamber to decrease cost lower than convention CVD chambers.Further, such deposition method for metal 20 is site selectivedeposition with respect to a selected portion of substrate 20, can fillultra-small openings, is not sensitive to a wetting property ofsubstrate 4, void-free filling for micro-via applications, formsthree-dimensional metallic nanostructures, works for a wide range ofdifferent primary reagents 62, amenable to deposit pure metals oralloys, amenable to produce carbon-free metal 20, and the like.

According to an embodiment, vapor deposition composition 60 thatincludes metal cation 64 to form metal 20 on substrate 4 providesdeposition of zero-dimensional, one-dimensional, two-dimensional, orthree-dimensional structures of metal 20 on substrate 4; deposition ofzero-dimensional, one-dimensional, two-dimensional, or three-dimensionalstructures of metal 20 that includes an oxide of the metal, depositionof zero-dimensional, one-dimensional, two-dimensional, orthree-dimensional structures of metal 20 composite structures of metal20 (e.g., metal in combination with a filler such as nanoparticles,e.g., nanotubes) or alloys of the metal; and the like.

In an embodiment, vapor deposition composition 60 that includes metalcation 64 to form metal 20 on substrate 4 provides selection of primaryreagent 62 or activating catalyst 28 to deposit pure metals or alloysfor metal 20. Further, metal 20 can be formed with a selected size,e.g., less than 1 nm in size and can fill a via from the bottom up, formin a micro-via or nano-via, fabricate a photonic structure, fabricate anantenna (e.g., for communications equipment), fabricate a circuit pathfor an electronic article, fabricate a magnetic structure (e.g., for amicroelectronics device or process), and the like. Additionally,processes for forming metal 20 can be controlled such as independentlyregulating a flow rate or vapor pressure, pre-heating temperature,concentration, or deposition rate of deposition composition 60 and itscomponents (e.g., 64, 66), and the like. In this manner, the processprovides control of morphology, crystallinity, grain size, thickness,deposition rate, precursor composition, and the like of metal 20 onsubstrate 4.

It is contemplated that the deposition of metal 20 on substrate 4 can beused to make lenses with high-Z metals (high atomic number) or fillingdefects in substrates such as cracks in ship hulls or bridges where thesubstrate is a metal that may have been subject to stress fracture orcorrosion. Further, such deposition is useful for producing devices andarticle for microelectronics, microelectromechanical systems (MEMS),microfluidics, bioactive substrates, bioremediation, and the like.

It is contemplated that in processes herein, substrate 4 is asemiconductor material that includes an element from group III, groupIV, group V of the periodic table, or a combination comprising at leastone of the foregoing elements. Activating catalyst 28 can include aplurality of metal catalysts, e.g., different metal catalysts. Theplurality of metal catalysts can include a plurality of differentshapes, different sizes, or combination comprising at least one of theforegoing shapes or sizes. In some embodiments, the plurality of metalcatalysts comprises gold, platinum, palladium, tungsten, silver, orcombination comprising at least one of the foregoing. It is contemplatedthat the etchant oxidizer includes an oxidant that is reduced byactivating catalyst 28, and the activatable etchant includes a reducingcompound that is oxidized by substrate 4.

With reference to coating 22, the plurality of dendritic veins 24 arehollow in some embodiments. Coating 22 can be an antireflective coatingthat has a reflectivity tuned from 10% to 0.01% at a wavelength from 30nm to 1 cm. Additionally, coating 22 can be an antireflective coatingthat is a broadband antireflective coating being antireflective to awavelength from 30 nm to 1 cm. The gradient in the density of the volumeof coating 22 can be a uniform gradient in the density of the volume,and coating 22 can have a gradient in an index of refraction. Thegradient in the index of refraction can be a uniform gradient thatvaries from 1 to 3.9. Furthermore, a temperature of substrate 4 duringthe oxidation-reduction reaction can be less than 150° C.

In some embodiments of forming metal 20 on substrate 4, a melting pointof primary reagent 62 can be less than 500° C., specifically less than250° C., and more specifically less than room temperature. While primaryreagent 62 dissociates to provide metal cation 64 and reducing anion 66,primary reagent 62 has high thermal stability with respect todecomposition to form a decomposition product that is different thandissociation products such as metal cation 64 and reducing anion 64.That is, primary reagent 62 withstands prolonged heating (several hoursor even days) at a temperature of 100° C. and greater, e.g., 300° C.,without significant thermal decomposition. Primary reagent producesmetal cation 64 and reducing agent 66 that independently have asufficient volatility to form vapor deposition composition 60 so thatmetal cation 64 will exit liquid medium 30, enter a vapor phase in vapordeposition composition 60, and contact substrate 4 or activatingcatalyst 28. Primary reagent 62 can be air-stable or can have a limitedsensitivity for air or moisture.

The articles and processes herein are illustrated further by thefollowing Examples, which are non-limiting.

EXAMPLES Example 1 Production of Etch Voids

Producing etch voids in a silicon substrate was investigated. Weresearched an etch rate of Ag, Au, and Pd/Au catalysts at one etchantcomposition. The etching process did not form a layer ofmeso/microporous silicon preceding disposition of the metal catalyst onthe substrate. We found that the catalyst traveled through athree-dimensional volume in the substrate and formed helical-shaped etchvoids therein.

Samples were prepared from p-type, 100-mm diameter (100) silicon wafersused with an as-manufactured stated resistivity of 5-10 Ωcm. Ag, Au, andPd/Au (40/60 atomic percent) were deposited on separate wafers using anelectron beam evaporator for a target thickness of 2.3-3.0 nm at adeposition rate of 0.15 nm/s and then 1 cm×1 cm samples were scribedfrom the larger wafer. Immediately prior to etching, samples werecleaned with an O₂ plasma or a piranha mixture of 3:1 sulfuricacid:H₂O₂.

Samples were etched with the vapor coming from a ρ=70^(12.8) etchantsolution made with 16 mL of 48 wt % HF and 18.4 mL of 30 wt % H₂O₂. Notethat ρ^(x) is used to denote the etchant composition whereρ^(x)=([HF]/([HF]+[H₂O₂]))^(x=[HF]) and x is the HF concentration inunits of moles/liter. The etchant was held at room temperature (≈27°C.), and the samples were held approximately 25 mm above the etchant byuse of an HF-compatible static chuck with substrate temperature control.

To evaluate the etch rate as a function of time, samples were etched at40° C. for different times (15 min, 30 min, 45 min, or 60 min). Toevaluate the influence of temperature, Au catalysts were used as thesubstrate was exposed for etching for 15 min at 35° C., 40° C., 45° C.,50° C., 55° C., or 60° C. Formation of microporous silicon using a vaporcomposition (as etchant) versus using a liquid medium (as etchant) wasstudied by comparing samples etched with the vapor composition at 35° C.held in the static chuck with samples held at room temperature above thesolution. The sample held at room temperature forms a thicker condensedliquid layer that is visible to the eye. Ag catalyst dissolution andre-deposition was confirmed by using electron-beam lithography topattern Ag and Au catalysts that were approximately 65 nm thick.

Top-down and cross-section images of the samples were taken using theIn-Lens detector of a Ziess LEO 1525 Thermally-Assisted ScanningElectron Microscope (SEM) to determine etch depth, etch rate, holemorphology, and microporous silicon generation.

Silicon coated with metal catalysts and exposed to a vapor mixture of HFand H₂O₂ exhibited etching confined to a 1-2 nm region surrounding thecatalyst with the etching process propagated by catalyst motion throughthree-dimensional space. Scanning electron microscope (SEM) micrographsof samples are shown in FIGS. 19A, 19B, 19C, and 19D for vaporcomposition etching of Si with Ag catalyst that respectively were etchedfor 15 min (19A), 30 min (19B), 45 min (19C), and 60 min (19D).

Similarly, FIGS. 20A, 20B, 20C, and 20D show scanning electronmicroscope (SEM) micrographs of samples for vapor composition etching ofSi with Au catalyst that respectively were etched for 15 min (20A), 30min (20B), 45 min (20C), and 60 min (20D).

Additionally, FIGS. 21A, 21B, 21C, and 21D show scanning electronmicroscope (SEM) micrographs of samples for vapor composition etching ofSi with Pd/Au catalyst that respectively were etched for 15 min (21A),30 min (21B), 45 min (21C), and 60 min (21D).

Catalysts randomly etched through three-dimensional volumes with sixdegrees of freedom. Catalysts were observed over a wide range of depthswithin a single sample, and a small percentage of the catalyst particlesetched perpendicular to the catalyst surface over an entire etch time. Alarge proportion of catalysts remained within a top 1-2 μm of thesurface of the sample.

FIG. 22 shows a graph of etch depth versus etch time for a mean observedetch depth for the three catalysts studied and a linear fit used toestimate an average etch rate for each catalyst. FIGS. 23A, 23B, and 23Cshow graphs of etch depth versus etch time for a distribution of wherecatalyst particles were observed and also show fits from FIG. 22. A widedistribution of observed etch depth was attributed to catalyst particlesetching through a three-dimensional volume in a random direction. Etchdepth data and rate data are summarized in TABLE I. Etching was absentin areas of sample that did not having disposed catalyst.

TABLE 1 Mean/Max Mean/Max Etch Depth [μm] Etch Rate Catalyst 15 min 30min 45 min 60 min [nm/min] Ag 0.45/0.91 0.87/1.37 1.20/2.08 1.94/3.3031/52  Au 1.72/2.50 2.88/3.17 3.81/4.24 4.91/6.81 70/110 Pd/Au 1.75/2.533.88/4.90 4.58/5.90 5.81/7.27 96/120

The metal catalyst propagated the etching reaction. For the liquidmedium (4:1.3:2.7 HF:H₂O₂:H₂O), Ag, Au, and Pd catalysts etched at 0.3,5.0, and >30 μm/min in a ρ=90^(13.8) such that etch rate wasproportional with the catalytic activity of the metal. For the vaporcomposition, etch rates of Ag, Au, and Pd/Au were 0.03, 0.07, and 0.10μm/min.

The etch rate of the vapor composition depended on substratetemperature. The etch depth and rate data for Au catalyst samples etchedfor 15 minutes at substrate temperatures from 35° C. to 60° C. above aρ=70^(12.8) solution are shown in FIG. 24 as a graph of etch depth andetch rate versus etch temperature. The maximum etch rate occurred at atemperature of 40° C.

Example 2 Catalyst Motion

The motion of the catalyst during the vapor composition etching of thesamples according to Example 1 was studied. Catalysts traveled throughthree-dimensional volumes during the etching process, as exemplified bythe helical structure shown in FIG. 25. Accordingly, the vaporcomposition etching of the samples showed that the vapor compositionformed complex structures without stiction issues. It is believed thatcatalyst motion during etch could be controlled to etch solely in avertical dimension by adjusting the HF and H₂O₂ concentrations withinthe incoming vapor or adjusting the catalyst shape andparticle-to-particle spacing. The feature resolution in FIG. 25 washigh, and a shape of the etch void matched a shape of the catalyst.

Example 3 Microporous Silicon

For the studies described in Example 1, formation of micro- andmesoporous silicon during etching was considered. While liquid mediumetching produced microporous silicon, the vapor composition etched thesamples but did not generate micro/mesoporous. FIGS. 26A and 26B showsmicrographs for the etched samples using the liquid medium, and FIGS.27A and 27B shows micrographs for the etched samples using the vaporcomposition. Both sets of data was for the Pd/Au catalyst. The lightgrey/white areas surrounding the metal catalysts (bright white)indicated the formation of microporous silicon in FIGS. 26A and 26B forthe liquid medium etching. These light-grey areas were missing in thesamples etched by the vapor composition as shown in FIGS. 27A and 27B,which indicated that the vapor composition etching did not generatemicroporous silicon. Both of these samples consisted of 2.3 nm of Pd/Audeposited at the same time in an e-beam evaporator, then etched abovethe same ρ=70^(12.8) mixture. The liquid medium etching was conducted byleaving the substrate at room temperature (˜27° C.) to create acondensed layer on the substrate that is thick enough to slightly beadup on the surface. This thickly condensed layer had a similar etchantcomposition and concentration as compared to the vapor compositionetching, yet resulted in a different morphology. The light grey areassurrounding the metal catalyst in FIGS. 26A and 26B were indicative ofmicro/mesoporous silicon generation, establishing that the liquid mediumetching with a Pd/Au catalyst generated micro/mesoporous silicon evenfor extremely dilute etchant compositions. However, increasing thesubstrate temperature reduced the condensed phase thickness to 1-2 nm,while maintaining the same etchant composition. As shown in FIGS. 27Aand 27B, these samples did not have micro/mesoporous silicon.

Example 4 Vapor Deposition

FIGS. 28A and B show before and after scanning electron microscopeimages of a structure etched using vapor-phase metal-assisted chemicaletching followed by vapor phase deposition of metal. FIG. 28A shows theetch wafer of silicon with etch voids across the surface. FIG. 28B showsnickel deposited into these voids by to fill the voids and cover thesurface. The nickel appeared as bright white with small cracks in thesurface caused when nickel depositions from neighboring voids met.Etching confined the nickel deposit to narrow locations where catalystwas present, which increased ease of identification of locations wherenickel deposited.

Example 5 Forming Etch Void and Forming Metal in Etch Void

A complex shape is fabricated in an substrate using a catalyst with acomplex shape. With reference to FIGS. 29A, 29B, 29C, and 29D, a “star”shaped catalyst is fabricated using electron beam lithography andelectron beam deposition. The catalyst is composed of two layers, afirst layer of Ti and a second layer of Au. The substrate and catalystare immersed in a ρ=90^([13.8]) etchant solution at room temperature fora few minutes. The resulting etch void is shaped like a spiraling star.The catalyst is left in a bottom of the etch void and is a whitishregion in a center of the void. The spiraling structure rotatescounter-clockwise as shown by “shadows” in the scanning electronmicroscope image. Varying the shape of the catalyst, composition of theetchant, and phase of the etchant affects the shape of the etch void.

While one or more embodiments have been shown and described,modifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention. Accordingly, it is to beunderstood that the present invention has been described by way ofillustrations and not limitation. Embodiments herein can be usedindependently or can be combined.

Reference throughout this specification to “one embodiment,” “particularembodiment,” “certain embodiment,” “an embodiment,” or the like meansthat a particular feature, structure, or characteristic described inconnection with the embodiment is included in at least one embodiment.Thus, appearances of these phrases (e.g., “in one embodiment” or “in anembodiment”) throughout this specification are not necessarily allreferring to the same embodiment, but may. Furthermore, particularfeatures, structures, or characteristics may be combined in any suitablemanner, as would be apparent to one of ordinary skill in the art fromthis disclosure, in one or more embodiments.

All ranges disclosed herein are inclusive of the endpoints, and theendpoints are independently combinable with each other. The ranges arecontinuous and thus contain every value and subset thereof in the range.Unless otherwise stated or contextually inapplicable, all percentages,when expressing a quantity, are weight percentages. The suffix “(s)” asused herein is intended to include both the singular and the plural ofthe term that it modifies, thereby including at least one of that term(e.g., the colorant(s) includes at least one colorants). “Optional” or“optionally” means that the subsequently described event or circumstancecan or cannot occur, and that the description includes instances wherethe event occurs and instances where it does not. As used herein,“combination” is inclusive of blends, mixtures, alloys, reactionproducts, and the like.

As used herein, “a combination thereof” refers to a combinationcomprising at least one of the named constituents, components,compounds, or elements, optionally together with one or more of the sameclass of constituents, components, compounds, or elements.

All references are incorporated herein by reference.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. “Or” means “and/or.” Further, the conjunction “or” is used tolink objects of a list or alternatives and is not disjunctive; ratherthe elements can be used separately or can be combined together underappropriate circumstances. It should further be noted that the terms“first,” “second,” “primary,” “secondary,” and the like herein do notdenote any order, quantity, or importance, but rather are used todistinguish one element from another. The modifier “about” used inconnection with a quantity is inclusive of the stated value and has themeaning dictated by the context (e.g., it includes the degree of errorassociated with measurement of the particular quantity).

What is claimed is:
 1. An article comprising: a substrate; and a coating disposed on the substrate that comprises: a microporous layer; a gradient in a density of a volume of the microporous layer; and a plurality of dendritic veins that are anisotropically disposed in the coating.
 2. The article of claim 1, wherein the coating is an antireflective coating.
 3. The article of claim 1, wherein the substrate and coating independently comprise a semiconductor material.
 4. The article claim 3, wherein the semiconductor material comprises an element from group III, group IV, group V of the periodic table, or a combination comprising at least one of the foregoing elements.
 5. The article of claim 4, wherein the substrate and the coating are an identical semiconductor material.
 6. The article of claim 1, wherein the plurality of dendritic veins are hollow.
 7. The article of claim 1, wherein a catalyst is disposed in a dendritic vein.
 8. The article of claim 1, wherein the coating has a reflectivity tuned from 10% to 0.01% at a wavelength from 30 nm to 10 cm.
 9. The article of claim 2, wherein the antireflective coating is a broadband antireflective coating being antireflective to a wavelength from 30 nm to 10 cm.
 10. The article of claim 1, wherein the gradient in the density of the volume is a uniform gradient in the density of the volume.
 11. The article of claim 10, wherein the coating further comprises a gradient in an index of refraction.
 12. The article of claim 11, wherein the gradient in the index of refraction is a uniform gradient that varies from 1 to 3.9.
 13. A process for forming a coating, the process comprising: disposing an activating catalyst on a substrate; introducing an activatable etchant; introducing an etchant oxidizer; performing an oxidation-reduction reaction between the substrate, the activatable etchant, and the etchant oxidizer in a presence of the activating catalyst, the oxidation-reduction reaction occurring in a liquid medium comprising: the activatable etchant; and the etchant oxidizer; forming an etchant product comprising a plurality of atoms from the substrate; removing a portion of the etchant product from the substrate; and forming a dendritic vein in the substrate to form the coating, the dendritic vein being anisotropically disposed in the coating.
 14. The process of claim 13, further comprising forming a gradient in a density of a volume of the coating.
 15. The process of claim 14, further comprising controlling an index of refraction of the coating to produce the coating with a uniform gradient in the index of refraction that varies from 1 to 3.9.
 16. The process of claim 14, further comprising controlling a reflectivity of coating.
 17. The process of claim 16, wherein the coating has a reflectivity tuned from 10% to 0.01% at a wavelength from 30 nm to 10 cm
 18. The process of claim 14, wherein a temperature of the substrate during the oxidation-reduction reaction is less than 150° C.
 19. A process for forming a coating, the process comprising: disposing an activating catalyst on a substrate; introducing an activatable etchant; subjecting the activating catalyst and the activatable etchant to an electric potential; performing an electrochemical reaction between the substrate and the activatable etchant in a presence of the activating catalyst and the electric potential, the electrochemical reaction occurring in a liquid medium comprising: the activatable etchant; and the etchant oxidizer; forming an etchant product comprising a plurality of atoms from the substrate; removing a portion of the etchant product from the substrate; and forming a plurality of dendritic veins in the substrate to form the coating, the plurality of dendritic veins being anisotropically disposed in the coating.
 20. The process of claim 19, wherein a temperature of the substrate during the electrochemical reaction is less than 150° C. 